URBANA 


ILLINOIS  STATE  GEOLOGICAL  SURVEY 


3  3051  00000  2133 


STATE  OF  ILLINOIS 

DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON.  Director 

DIVISION  OF  THE 
STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON,  Chief 


BULLETIN  NO.  49 


GEOLOGY  AND  MINERAL  RESOURCES  OF  THE 
DIXON  QUADRANGLE 

BY 

RUSSELL  STAFFORD  KNAPPEN 


PRINTED   BY  AUTHORITY  OF  THE   STATE   OF  ILLINOIS 


URBANA,  ILLINOIS 
1926 


fLLFNOfS  GEOLOGICAL 
SURVEY  LIBRARY 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  Illinois  Urbana-Champaign 


http://archive.org/details/geologymineralre49knap 


£  en 

Vs-6  .  A^ 


Xv-X^ 


d.\ 


STATE  OF  ILLINOIS 

DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON,  Director 

DIVISION  OF  THE 

STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON,  Chief 


Committee  of  the  Board  of  Natural  Resources 
and  Conservation 

A.  M.  Shelton,  Chairman 

Director    of   Registration    and    Education 

Charles  M.  Thompson 

Representing   the    President    of   the    Uni 
versity  of  Illinois 

Edson  S.  Bastin 
Geologist 


Schnepp  &  Barnes,  Printers 

Springfield,  III. 

1926 

56288— 3M 


CONTENTS 

PAGE 

Chapter  I — Introduction    11 

Location   and    area 11 

Previous  work    11 

Field   work    12 

Acknowledgments    12 

Geography  of  the  quadrangle 13 

Physiographic    province    13 

Climate    and    vegetation 13 

Topography    13 

Elevation    and    relief 13 

Upland  plain   13 

Valleys    14 

Till  valleys    14 

Lim'estone  valleys   14 

Sandstone  valleys    15 

Valleys   in   sandstone   with   overlying   limestone 15 

Flood-plains   and  terraces 16 

Drainage     16 

Culture    18 

Distribution    of    population 18 

Industry    IS 

Transportation   and   communication 18 

Chapter  II — Geologic  terms  and  principles 19 

Topographic   map    19 

Land  divisions    20 

General  geologic  principles 21 

Rocks     21 

Weathering    22 

Erosion    22 

Marine  deposition    23 

Stratification    23 

Clastics    24 

Limestone     24 

Dolomite     24 

Continental  deposition  25 

Eolian   deposits    25 

Stream   deposits    25 

Lake  deposits   26 

Glacial  deposits   26 

Eskers    27 

Drift    27 

Consolidation   of  sediments 27 

Ground  water   2S 

5 


PAGE 

Chapter  II — Geologic  terms  and  principles — Concluded. 

Historical    geology    2S 

Geologic    time    table 28 

Correlation     28 

Physiographic   cycle    30 

Chapter  III — Stratigraphy    32 

Pre-Cambrian   rocks    34 

Crystallines    34 

Keweenawan    (  ? )    sandstone 34 

Paleozoic    group     36 

Cambrian    system    36 

Croixan   series    36 

Ordovician    system    39 

Prairie  du   Chien  series 39 

Oneota   dolomite    39 

Name    39 

Lithology    40 

Areal   distribution    40 

Correlation     40 

"New   Richmond"    sandstone 40 

Name     40 

Lithology    41 

Topographic    expression    42 

Thickness 42 

Areal   distribution    42 

Correlation  and  relation  to  adjacent  formations 42 

Shakopee  dolomite    43 

Name  and   lithology 43 

Topographic  expression,  thickness  and  areal  distribution.  45 

Paleontologic   character    46 

Correlation    47 

Relations  to   adjacent   formations 47 

Middle   Ordovician    series 48 

St.   Peter   sandstone 48 

Name    4S 

Lithologic    character    48 

Topographic    expression    50 

Thickness  and   areal   distribution 50 

Paleontologic  character  and  correlation 51 

Relations  to  adjacent  formations 51 

Glenwood    shale    52 

Name    and    character 52 

Topographic    expression    52 

Thickness    52 

Areal  extent    53 

Age.   correlations   and   relations 53 

Platteville  limestone    53 

Name    53 

Lithologic   character    53 

Topographic   expression    55 

Thickness  and  details  of  section 55 

6 


PAGE 

Chapter  III — Stratigraphy — Concluded. 

Areal  distribution    58 

Paleontologic    character    58 

Correlation     60 

Relations  to  adjacent  formations 60 

Galena   dolomite    61 

Name    61 

Lithologic    character    61 

Topographic    expression    62 

Thickness    62 

Areal   distribution    64 

Paleontologic    character    64 

Correlation     65 

Relations  to  adjacent  formations 65 

Younger    Paleozoic    formations 65 

Cenozoic  group 66 

Pleistocene  system    66 

Pre-Illinoian  deposits   66 

Illinoian  and  Iowan   (?)   tills 67 

Introduction    67 

Age  of  the  till 70 

Grand  Detour  esker 73 

Loess    74 

Lithology 74 

Topographic    expression    75 

Thickness    75 

Area    75 

Age     75 

Early  Wisconsin  valley  train 76 

Late   Wisconsin    valley   train 77 

Backwater  deposits    78 

Recent    sediments    78 

Flood-plain    alluvium    78 

Peat    and    muck 78 

Sand    dunes    79 

Chapter  IV — Geologic    history    SO 

Introduction    80 

Pre-Cambrian   eras    80 

Paleozoic   era    80 

Cambrian  period    80 

Ordovician  period   81 

Lower  Ordovician  or  Prairie  du  Chien  epoch SI 

Oneota  stage  81 

"New   Richmond"    stage 81 

Shakopee   stage    82 

Middle  Ordovician   epoch 85 

St.    Peter    stage 85 

Glenwood  stage 86 

Platteville  stage    87 

Galena   stage    89 

7 


PAGE 

Chapter  IV — Geologic  history — Concluded. 

Later   Paleozoic  record 90 

Cenozoic    era    90 

Tertiary  peneplanation    90 

Pleistocene    period    94 

Pre-Illinoian   time    94 

Illinoian  glaciation    95 

Sangamon   interglacial   epoch 96 

Iowan    glacial    epoch 96 

Peorian    interglacial    epoch 96 

Wisconsin  epoch    , 97 

Post-Illinoian    drainage    development -. 98 

Recent  history    101 

Asymmetrical  valley  slopes,  stream  displacement  and  exposure  to 

sun    and    wind 102 

Human  activities  and  their  erosional  effects 104 

Chapter  V — Structural   geology    107 

General    statement    107 

Structure-contour  map 107 

Structure  of  the  quadrangle 109 

Origin    of   the   structure 110 

Pre-St.    Peter    structure Ill 

Faulting     Ill 

Chapter  VI — Mineral   resources    112 

General    statement    112 

Water    112 

Surface   water    112 

Ground  water   113 

Water  for  vegetation 113 

Springs    113 

Shallow  wells  in  till 114 

Wells  in  limestone 115 

Wells  in  the  St.  Peter  sandstone 116 

Artesian   wells    117 

Cement   materials    119 

Limestone  and  limestone  products 122 

Glass   sand   125 

Sand   and   gravel 128 

Potash     129 

Petroleum     131 

Natural  gas   132 

Ore   minerals    132 

Sulphides    133 

Limonite     134 

Copper   and   gold 135 


ILLUSTRATIONS 

PLATE  PAGE 

I.     General  and  economic  geology  of  the  Dixon  quadrangle Pocket 

II.     Topographic  map  of  the  Dixon  quadrangle Pocket 

III.     Index  mlap  of  Illinois,  showing  location  of  the  Dixon  quadrangle  and  the 

meridians  and  base  lines 10 

IV.     Changes  in  Rock  River  and  its  tributaries,  resulting  from  Illinois  glaci- 

ation 98 

V.     Areal    geology    map    of    the    Dixon    quadrangle    with    structure    contours 

drawn  on  the  top  of  the  St.  Peter  sandstone 108 

FIGURE 

1.  Diagramatic  section  of  alluvial  and  rock-defended  terraces  in  Rock  River 

alluvium 17 

2.  Geologic  column   for  Dixon  quadrangle 32 

3.  Bar  cross-bedding  in  the  "New  Richmond"  sandstone 41 

4.  Typical  exposure  of  Shakopee  dolomite 44 

5.  Weathered  bluff  of  St.  Peter  sandstone 49 

6.  Bluff  of  St.  Peter  sandstone  east  of  Green  Rock 49 

7.  Outcrop  of  Platteville  limestone 55 

8.  Galena  dolomite  showing  typical  massive  beds  which  weather  to  thinner 

strata    62 

9.  Close  view  of  exposure  in  figure  8 63 

10.  Gentle  folding  of  the  Shakopee  dolomite 84 

11.  Sharp  folding  and  fracturing  of  the  Shakopee  dolomite 85 

12.  Development  of  cuestas  and  their  relations  to  a  peneplain 92 

13.  Rock  River  valley  and  the  Tertiary  peneplain 93 

14.  Maximum  extension  of  North  American  ice-sheets 94 

15.  Conditions  producing  an  artesian  water  supply  for  the  Dixon  quadrangle   .118 

16.  Quarrying  of  the  Blue  limestone  at  the  plant  of  the   Sandusky  Cement 

Company .  120 

17.  Quarry  of  the  Sandusky  Cement  Company 121 

18.  The  mill  at  the  plant  of  the  Sandusky  Cement  Company 122 

19.  Sand  crushing  and  washing  plant  of  the  National  Silica  Company 126 

20.  Sand  pit  of  the  National  Silica  Company 126 


TABLES 

PAGE 

1.  Geologic  formations  33 

2.  Fossils  collected  from  the  Platteville  limestone 59 

3.  Wells  not  reaching  rock  in  the  southwestern  part  of  the  quadrangle 69 

4.  Wells  in  the  southwestern  part  of  the  quadrangle  with  depth  to  rock  only  70 

5.  Sink  holes  in  the  quadrangle 102 

6.  Elevations  of  top  of  St.  Peter  at  points  outside  Dixon  quadrangle  used  in 

preparing  structure  map 108 

7.  Analysis  of  water  in  200-foot  well  at  Dixon  State  Hospital 116 

8.  Analysis  of  Croixan  water  from  Dixon 119 

9.  Analyses    of    surface    and    washed    sand    from    quarry    of    National    Silica 

Company    127 

10.     Potash  content  of  samples  from  deposits  in  the  quadrangle 130 


10 


OF  THE 


>n  quadrangle, 
see  Plate  III) 
/  and  89°  30', 
It  is  approxi- 
:mare  miles. 


eology  of  Illi- 
f  the  area  or 
le  preparation 

34,   pp.   134-161, 

:rom   Oregon  to 

lois,  vol.   5,   PP. 

ois,    vol.    5,    pp. 

Geol.,  vol.   5,   p. 

e  in  northwest- 

ey    Seventeenth 

Illinois:    Amer. 

issippi    Valley: 

18,  798  pp.,  1899. 
Survey  Bull.  1, 

Dl.   Survev  Bull. 


10. 


Geologic  formal 
Fossils  collectec 
Wells  not  reach 
Wells  in  the  soi 
Sink  holes  in  t 
Elevations  of  tc 

preparing  str 
Analysis  of  wat 
Analysis  of  Crc 
Analyses    of    su 

Company  .  .  . 
Potash  content 


GEOLOGY  AND   MINERAL   RESOURGES   OF  THE 
DIXON  QUADRANGLE 

By  Russell  Stafford   Knappen 


CHAPTER  I— INTRODUCTION 

Location  and  Area 

The  area  described  in  this  report  is  known  as  the  Dixon  quadrangle. 
It  is  situated  in  Lee  and  Ogle  counties  in  northern  Illinois  (see  Plate  III) 
and  is  limited  on  the  east  and  west  by  the  meridians  of  89°  15'  and  89°  30', 
and  on  the  north  and  south  by  the  parallels  42°  and  41°  45'.  It  is  approxi- 
mately 17.3  miles  long  and  12.9  miles  wide  and  covers  223  square  miles. 

Previous  Work 

In  addition  to  papers  dealing  in  general  terms  with  the  geology  of  Illi- 
nois, the   following  publications  describe  specific  portions   of   the   area   or 
special  problems  relating  to  it  and  have  been  consulted  in  the  preparation 
of  this  report. 
Shepard,  C.  U.,  Geology  of  upper  Illinois:    Amer.  Jour.  Sci.,  vol.   34,  pp.   134-161, 

1838. 
Everett,   Oliver,  Geology  of  a   section  of  the   Rock  River  valley  from   Oregon  to 

Sterling:   Illinois  Nat.  Hist.  Soc.  Trans.,  vol.  1,  pp.  53-58,  1861. 
Shaw,  Hon.  James,  Geology  of  Lee  County:    Geol.  Survey  of  Illinois,  vol.   5,   pp. 

124-139,  1873. 
Geology    of    Ogle    County:    Geol.    Survey    of    Illinois,    vol.    5,    pp. 

104-123,  1873. 
Tiffany,  A.  R.,  Record  of  a  deep  well  at  Dixon,   Illinois:    Amer.  Geol.,   vol.   5,  p. 

124,  1890. 
Hershey,  Oscar  H.,  The  Elkhorn  Creek  area  of  St.  Peter  sandstone  in  northwest- 
ern Illinois:  Amer.  Geol.,  vol.  14,  pp.  169-179,  1894. 
Leverett,    Frank,    Water    resources    of    Illinois:    U.    S.    Geol.    Survey    Seventeenth 

Ann.  Rept.,  Pt.  2,  pp.  695-849,  1896. 
Hershey,    Oscar   H.,    Preglacial    erosion    cycles    in    northwestern    Illinois:    Amer. 

Geol.,  vol.  18,  p.  71,  1896. 
Physiographic    development    of    the    upper    Mississippi    Valley: 

Amer.  Geol.,  vol.  20,  p.  246,  1897. 
Leverett,  Frank,  The  Illinois  glacial  lobe:  U.  S.  Geol.  Survey  Mon.  38,  798  pp.,  1899. 
Weller,  Stuart,  The  geological  map  of  Illinois:   Illinois  State  Geol.  Survey  Bull.  1, 

1906. 
Geologic  structure  of  the  State:    Illinois  State  Geol.  Survey  Bull. 

2,  1906. 

11 


VI  DIXON    QUADRANGLE 

Geological   map    of   Illinois:    Illinois    State   Geol.    Survey    Bull.    6, 

pp.    1-34,    1907,    (especially   map). 
Udden,   Jon   A.   and   Todd,   J.   E.,    Structural   materials    in    Illinois:    Illinois    State 

Geol.  Survey  Bull.  16,  Dixon  vicinity,  pp.  362-368,  1910.    (analyses). 
Bleininger,    A.    V.,    et    al,    Portland-cement    resources    of    Illinois:     Illinois    State 

Geol.  Survey  Bull.  17,  p.  87,  1912. 
Cady,  G.  H.,  The  structure  of  the  La  Salle  anticline;   Illinois  State  Geol.  Survey 

Bull.  36,  pp.  85-179,  1920. 


Field  Work 

The  field  work  for  this  report  occupied  July,  August  and  half  of  Sep- 
tember, 1919,  four  weeks  in  August,  1920,  and  three  weeks  in  May  and 
June,  1923.  While  the  general  distribution  of  formations  could  be  deter- 
mined readily,  the  heavy  cover  of  glacial  drift  in  many  places  obscured 
boundaries  and  relations  of  formations.  Much  time  was  spent  in  finding 
good  exposures  in  critical  areas.  The  general  geologic  map  (Plate  I)  in- 
dicates the  actual  outcrops ;  additional  information  needed  in  compiling  the 
map  showing  areal  geology  and  structure  contours  (Plate  V)  was  obtained 
from  well  records. 

Acknowledgments 

This  study  was  proposed  by  Mr.  F.  W.  DeWolf,  former  Chief  of  the 
Illinois  State  Geological  Survey  and  the  late  Dr.  R.  D.  Salisbury,  Consult- 
ing Geologist.  The  author  desires  to  express  his  sincere  appreciation  of 
their  cordial  assistance  in  the  carrying  on  of  the  work. 

Dr.  Gilbert  H.  Cady,  of  the  Survey,  spent  two  days  in  the  field;  and 
two  field  conferences,  covering  six  days,  were  held  with  Dr.  M.  M.  Leigh- 
ton,  Pleistocene  Geologist,  and  present  Chief  of  the  Survey,  regarding  the 
Pleistocene  geology  of  the  quadrangle.  Dr.  J.  J.  Galloway  of  Columbia 
University,  New  York  City,  spent  three  days  in  field  consultation  on  strati- 
graphic  problems.  In  addition,  Dr.  Leighton  has  critically  read  the  sec- 
tions of  the  report  dealing  with  Pleistocene  problems,  making  many  helpful 
suggestions,  and  Drs.  Johnson,  Ogilvie  and  Galloway  of  Columbia  Uni- 
versity have  criticized  the  major  portion  of  the  report.  The  author  is  glad 
to  acknowledge  his  indebtedness  to  all  of  them  for  their  cordial  assistance. 

The  unfailing  helpfulness,  courtesy  and  good  will  of  the  citizens  of  the 
area  made  the  field  work  a  pleasure  and  contributed  much  to  its  accuracy 
and  completeness.  It  is  hoped  that  in  addition  to  adding  some  facts  to  gen- 
eral geologic  knowledge,  this  report  may  explain  many  local  features  and 
lead  to  a  better  understanding  of  and  greater  interest  in  the  geologic  history 
and  phenomena  of  the  area. 


INTRODUCTION  13 

Geography  of  the  Quadrangle 

PHYSIOGRAPHIC   PROVINCE 

The  Dixon  quadrangle  lies  in  what  is  known  physiographically  as  the 
Till  Plains  section  of  the  Central  Lowlands  Province.  Essentially  flat-lying 
beds  of  sedimentary  rock  underlie  the  area,  but  the  present  topography  is 
chiefly  the  product  of  glacial  deposition  and  stream  erosion,  which  are 
characteristic  of  the  Till  Plains  section  as  a  whole. 

CLIMATE  AND  VEGETATION 

The  climate  is  continental.  Summer  is  hot,  with  many  thunderstorms  ; 
winter  is  cold  and  invigorating,  but  not  severe.  The  temperature  ranges 
from  100°  F.  in  summer  to  -10°  in  winter.  The  mean  annual  precipitation 
amounts  to  about  33  inches. 

Vegetation  consisted  originally  of  prairie  grasses  on  the  uplands  and  a 
moderate  growth  of  deciduous  trees  along  the  valleys.  Little  of  the  original 
sod  now  remains,  corn,  wheat,  oats,  clover  and  other  farm  crops  having  re- 
placed the  prairie  grasses.  Around  the  farm  houses,  shade  and  hardy  fruit 
trees  have  been  planted. 

TOPOGRAPHY 

ELEVATION    AND   RELIEF 

The  quadrangle  as  a  whole  is  a  gently  rolling  plain,  rising  from  an  ele- 
vation of  ?80  feet  at  the  south  to  slightly  more  than  900  feet  above  sea 
level  at  the  northern  boundary.  The  highest  points  in  the  area  are  simply 
parts  of  this  upland  plain.  Ridge  Road  has  an  elevation  of  901  feet  in 
eastern  Pine  Creek  Township,  and  Devils  Backbone  in  Oregon  Township 
stands  905  feet  above  sea  level.  Many  of  the  surrounding  areas  approach 
the  same  elevation.  As  is  to  be  expected,  the  lowest  region  lies  along  the 
master  stream,  Reck  River.  This  stream  enters  the  quadrangle  at  an  eleva- 
tion of  658  feet  and,  falling  18  feet  in  23  miles,  leaves  it  at  an  elevation  of 
640  feet.  The  total  relief  of  the  quadrangle  is  265  feet.  A  relief  of  200 
feet  within  a  half  mile  is  not  uncommon  along  Rock  River. 

UPLAND   PLAIN 

A  very  gently  rolling  till  plain  which  rises  northward  about  8  feet  per 
mile  forms  the  upland  of  the  quadrangle,  and  extends  beyond  it  in  all  di- 
rections. Its  original  surface  is  so  nearly  level  that  many  sections  do  not 
have  a  relief  of  20  feet.  Rock  outcrops  are  few  on  this  plain,  and  where 
rock  occurs,  its  surface  blends  perfectly  with  the  upland  and  does  not  affect 
the  topography.  For  instance,  the  rock  now  exposed  in  quarries  in  sections 
28  and  30,  South  Dixon  Township,  was  discovered  in  plowing.  Originally, 
the  upland  extended  across  the  entire  area  with  minor  interruptions,  but  it 


14  DIXOX    QUADRANGLE 

has  been  severely  dissected  by  Rock  River  and  its  tributaries.  Rock  River 
valley  is  now  a  great  trough  extending  southwest  through  the  upland.  The 
valley  itself  averages  two  miles  in  width,  but  the  numerous  tributaries  have 
so  dissected  the  upland  that  it  now  covers  only  about  10  per  cent  of  the 
northwestern  half  of  the  quadrangle.  Traces  of  the  old  upland  persist  on 
the  stream  divides,  especially  where  limestone  is  present ;  but  these  remnants 
are  small.  The  southern  and  eastern  parts  of  the  quadrangle  have  not  been 
severely  eroded,  and  the  original  gently  rolling  till  surface  is  preserved  over 
large  areas  in  Bradford,  China.  Nachusa  and  South  Dixon  townships. 

VALLEYS 

The  upland  valleys  are  of  four  principal  types,  each  a  resultant  of  the 
varying  resistance  of  underlying  rocks  to  weathering  and  erosion.  So  pro- 
nounced are  the  characteristics  of  these  different  valleys,  that  the  kind  of 
material  in  which  each  has  been  excavated  usually  can  be  inferred  from  the 
topography.  The  four  classes  of  valleys  are  those  developed  in  (a")  till 
(b)    limestone   (c)    sandstone  and    id)    sandstone  with  overlying  limestone. 

TILL    VALLEYS 

Glacial  till  is  very  easily  eroded,  and  Avhere  conditions  are  favorable, 
narrow  valleys  develop  rapidly.  Gullies  six  to  eight  feet  deep,  and  more 
than  100  feet  long,  have  been  cut  in  a  single  season.  The  typical  till  valley 
is  not.  however,  narrow  and  steep-sided,  because  slope-wash  readily  erodes 
the  valley  sides,  often  carrying  down  to  the  bottom  of  the  valley  more  clay 
and  silt  than  the  temporary  wet-weather  stream  can  remove.  As  a  conse- 
quence, till  valleys  are  broadly  open,  with  gently  sloping  sides,  which  merge 
almost  imperceptibly  into  both  the  flat  alluvial  bottoms  and  the  upland  plain 
above.  Such  valleys  often  appear  shallow  and  of  slight  importance,  and 
only  after  considerable  contact  with  them  does  one  realize  that  they  are  fre- 
quently deeper  and  much  wider  than  the  sharper  and  more  impressive  rock 
vallevs.  Franklin  Creek,  southeast  of  Franklin  Grove,  and  Threemile  and 
Fivemile  branches  in  South  Dixon  Township  occupy  till  valleys. 

LIMESTONE    VALLEYS 

Limestone  and  soft  sandstone  are  the  only  important  rocks  exposed  in 
this  quadrangle.  Their  distribution  and  characteristics  are  described  in 
Chanter  111  and  the  general  geologic  map  (Plate  E)  shows  their  surface 
extent.      Each  type  of  rock  produces  a  distinctive  valley  form. 

In  a  limestone  region,  valleys  arc  deepened  slowly  because  the  streams 
cannot  readily  erode  the  solid  rock  of  their  channels.  Valley  sides  are 
worn  back  slowly  by  weathering,  and  in  time  their  slopes  become  gentle. 
Since  glaciation,  the  streams  in  this  region  have  deepened,  but  have  not 
materially  widened  the  limestone  channels.     Weathering  has  been  slow,  and 


INTRODUCTION  15 

consequently  the  valleys  in  limestone  have  rather  steep-sided  slopes  with 
little  or  no  flood-plain  areas.  The  valley  sides  commonly  meet  the  upland 
at  rather  pronounced  angles,  instead  of  merging  gradually  into  the  original 
surface,  as  do  the  till-valley  slopes.  Pine  Creek  has  a  typical  limestone 
valley  from  Stratford  east  to  The  Pines,  and  several  of  the  short  tributaries 
of  the  lower  Rock  River  have  developed  similar  limestone  valleys. 

SANDSTONE    VALLEYS 

The  chief  sandstone  of  the  area — the  St.  Peter — is  a  slightly  cemented, 
pure-quartz  sandstone.  Water  passes  through  it  readily ;  bare  fingers  can 
dig  in  a  fresh  exposure,  but  weathering  neither  dissolves  nor  readily  disin- 
tegrates the  rock.  Streams  erode  it  easily,  cutting  deep  valleys  quickly  and 
widening  them  by  removing  the  soft  sandstone  of  the  lower  valley  sides. 
Wind  erosion,  growth  of  plants,  and  movement  of  animals  combine  to  round 
off  the  upper  slopes  of  the  valley  wall,  but  do  not  materially  affect  the  lower 
parts,  which  are  kept  steep  or  vertical  by  the  undercutting  of  the  stream 
at  their  base.  The  normal  sandstone  valley,  accordingly,  has  a  wide  flood- 
plain,  and  valley  sides  which  are  steep  or  vertical  below,  but  more  gentle 
above,  passing  gradually  into  the  rounded  slopes  of  the  sandstone  hills. 
Characteristic  sandstone  valleys  are  those  of  lower  Franklin  and  Chamberlin 
creeks. 

VALLEYS     IN     SANDSTONE     WITH     OVERLYING     LIMESTONE 

Where  the  valley  has  been  cut  through  limestone  into  sandstone  below, 
a  broad  flood-plain  with  steep  lower  slopes  is  formed,  as  in  a  normal  sand- 
stone valley.  Stream  erosion  widens  the  valley  floor  in  the  sandstone  more 
rapidly  than  weathering  removes  the  capping  limestone  above,  and  as  the 
sandstone  is  cut  away,  the  unsupported  limestone  breaks  off  along  vertical 
joint  planes.  These  valleys,  then,  have  rather  wide  flood-plains,  vertical  or 
very  steep  walls  in  both  sandstone  and  limestone,  and  practically  no  grada- 
tion from  the  valley  wall  into  the  upland  surface,  except  where  the  over- 
lying till  is  thick.  Such  "box"  valleys  are  typical  of  western  tributaries  of 
Rock  River  above  Grand  Detour,  of  Pine  Creek,  and  of  Franklin  Creek 
for  two  miles  north  of  the  Chicago  and  Northwestern  Railway. 

Few  valleys  belong  exclusively  to  one  type.  Rock  River  valley  belongs 
to  all  four  types,  although  the  till  valley  is  poorly  developed.  At  the  north- 
ern boundary  and  for  two  miles  near  Grand  Detour,  there  is  a  till  valley ; 
from  Devils  Backbone  to  a  point  three  miles  below  Grand  Detour,  there  is 
a  normal  sandstone  valley  with  the  exception  of  two  miles  near  Grand  De- 
tour ;  at  Devils  Backbone  and  from  Pine  Creek  to  the  cement  plant,  two 
miles  above  Dixon,  the  valley  is  of  the  sandstone-with-overlying-limestone 
type,  and  from  the  cement  plant  westward,  Rock  River  has  a  limestone 
valley. 


16  DIXOX    QUADRANGLE 

From  Daysville,  near  the  north  boundary  of  the  quadrangle,  to  Dixon, 
the  valley  is  alternately  narrow  and  wide.  Sometimes  the  river  flows  be- 
tween steep,  unscalable  sandstone  cliffs,  which  rise  sheer  to  the  castellated 
limestone  rim  above.  Elsewhere,  the  bluffs  draw  back,  and  sometimes  al- 
most disappear,  while  rich  agricultural  land  lies  on  the  flood-plain.  Some 
of  the  variation  in  width  and  ruggedness  is  due  to  the  fact  that  the  valley 
consists  alternately  of  preglacial  and  postglacial  sections,  but  the  greater 
part  of  the  irregularity  is  due  to  the  varying  kinds  of  rock  in  which  the 
valley  lies. 

With  the  possible  exception  of  Illinois  Valley  in  the  vicinity  of  Starved 
Rock  State  Park,  no  more  beautiful  scenery  is  found  in  northern  Illinois 
than  along  the  deep,  almost  gorge-like  valley  of  Rock  River.  Grand  Detour, 
lying  in  the  center  of  the  "gorge,"  is  one  of  the  popular  summer  resorts  of 
the  State. 

FLOOD-PLAIXS    AND    TERRACES 

While  most  of  the  streams  are  still  actively  deepening  their  channels, 
many  of  the  larger  streams  are  developing,  or  flowing  upon,  flood-plains,  the 
extent  of  which  are  shown  on  Plate  I  by  the  deposits  of  alluvium. 

Rock  and  Kyte  River  valleys  were  once  filled  with  sand  and  gravel  to 
approximately  45  feet  above  the  present  streams.  The  origin  and  character 
of  these  valley  trains  are  discussed  on  page  76.  When  these  valleys  were 
buried  in  alluvium,  the  tributary  valleys  were  either  filled  to  this  same  level, 
or  were  ponded,  forming  temporary  lakes,  remnants  of  which  persist  as 
marshes  in  lower  Kyte  and  Franklin  valleys.  Ever  since  the  valley  trains 
were  formed,  Rock  River  and  its  tributaries  have  been  removing  the  filling. 
As  the  streams  erode  this  material,  they  SAving  back  and  forth  across  the 
alluvium,  forming  new  flood-plains  at  lower  le\*els.  Remnants  of  the  higher 
flood-plains  are  left  as  terraces  or  "second  bottoms"  on  the  valley  sides.  In 
the  western  part  of  Dixon,  four  distinct  terraces  are  recognizable,  each  rep- 
resenting a  step  in  the  removal  of  the  valley  train.  Usually  these  terraces 
result  from  the  river  swinging  back  before  completing  a  traverse  across  the 
entire  flood-plain;  sometimes,  as  in  the  case  of  the  terrace  on  which  the  milk 
condensery  stands  in  North  Dixon,  rock  interrupts  the  swing  and  a  rock- 
defended  terrace  results.  Figure  1  shows  diagrammatically  the  develop- 
ment of  these  two  types  of  terraces,  common  in  the  broader  parts  of  Rock 
and  Kyte  valleys.  Ordinary  alluvial  terraces  are  present  in  all  the  wider 
parts  of  the  Rock  River  valley. 

DRAINAGE 

The  entire  quadrangle  is  well  drained  by  Rock  River  and  its  tributaries, 
of  which  Kyle  River  and  Pine  Creek  arc  perennial  streams  throughout  their 
courses  in  the  quadrangle.     Other  permanent  streams  have  their  headwaters 


INTRODUCTION 


17 


within  the  area,  and  consequently  are  intermittent  in  their  higher  reaches. 
Gagings  of  Rock  River  have  not  been  made  in  this  area,  so  far  as  the  writer 
can  learn,  but  accurate  records  are  available  for  the  four  years  1914  to 
1918  at  Rockford,  35  miles  upstream,  and  at  Lyndon,  the  same  distance 
downstream1.  From  these  records,  it  appears  that  the  average  flow  of 
Rock  River  in  this  quadrangle  is  approximately  6,000  second-feet  (cubic 
feet  per  second),  the  average  flood  discharge  is  25,000  second-feet,  and 
average  low-water  discharge,  1,300  second-feet.  The  lowest  water  during 
the  four  years  was  about  500  second-feet,  and  the  greatest  flood  discharge 
was  35,000  second-feet  in  March,  1916.  High-water  stage  normally  comes 
in  March,  when  melting  snows  and  spring  rains  are  adding  to  the  stream 
flow,  with  a  second,  but  much  lower,  high-water  stage  in  September  or 
October,  following  the  fall  rains.  Low-water  normally  occurs  in  July  or 
August,  when  precipitation  is  low  and  evaporation  of  ground  and  stream 
water  is  greatest,  and  a  second  low-water  stage  occurs  in  January,  when 
precipitation  accumulates  on  the  surface  as  snow,  and  frozen  soil  retains  the 
ground  water. 


Fig.  1.    Diagramatic  section  of  alluvial  and  rock-defended  terraces  in  Rock  River 

alluvium. 

In  general,  only  the  deeper  and  larger  valleys  have  permanent  streams. 
If  the  underlying  rock  is  sandstone,  the  valley  must  be  deeper,  and  the 
drainage  basin  larger,  in  order  to  support  a  permanent  stream,  than  if  the 
valley  is  in  limestone.  This  condition  is  caused  by  the  greater  perviousness 
of  the  sandstone,  and  the  more  ready  flow  of  water  through  it,  resulting  in 
more  gentle  slopes  of  the  ground- water  table  and  a  more  ready  absorption 
of  water  in  the  St.  Peter  areas. 

A  very  small  portion  of  the  area  is  drained  by  sub-surface  streams 
through  limestone.  This  drainage  has  produced  sink  holes  in  section  27  and 
adjacent  sections  of  Dixon  Township  and  in  section  18,  LaFayette,  and  sec- 
tion 19,  Ashton  Township. 

Two  small  depressions,  neither  exceeding  live  feet  in  depth  or  three 
acres  in  area,  lie  south  of  Chicago  and   Northwestern    Railway   in   sees.    1 0 


1  Surface  water  supply   of   tli<>    lTniWd    States,    1918:    r.    S.    Geol.    Survey    Water-Sup- 
ply Paper  475,  p.  98,  1921. 


18  DIXON    QUADRANGLE 

and  11,  South  Dixon  Township.  In  the  lower  parts  of  Kyte  and  Franklin 
valleys  are  marshes  which  have  resulted  from  the  aggrading  of  Rock  River 
(page  78). 

CULTURE 

DISTRIBUTION    OF   POPULATION 

The  Dixon  quadrangle  is  essentially  an  agricultural  region.  About  29 
per  cent  of  the  population  live  on  farms.  Dixon,  which  had  8,201  inhabit- 
ants in  1920,  is  the  only  city,  and  contains  about  58  per  cent  of  the  popula- 
tion of  the  quadrangle.  Approximately  13  per  cent  live  in  the  villages  of 
Franklin  Grove,  Grand  Detour,  Nachusa,  Eldena,  Daysville,  Honey  Creek, 
Stratford,  and  part  of  Lee  Center. 

INDUSTRY 

Farming,  including  cattle  raising,  is  the  principal  industry  of  the  area. 
The  newly- formed  glacial  soil  of  the  till  plains  makes  Illinois  one  of  the 
richest  agricultural  regions  of  the  country.  The  till-covered  areas  are  the 
most  fertile;  limestone  provides  a  rich  but  often  stony  soil,  while  areas  of 
exposed  sandstone  are  normally  dry  and  less  productive  than  the  rest  of  the 
quadrangle. 

Dixon  is  an  important  manufacturing  city  producing  a  wide  variety  of 
products,  chief  of  which  is  cement.  Of  the  mineral  resources  developed  in 
the  area,  those  used  in  the  manufacture  of  cement  rank  first  in  importance. 
Next  in  importance  is  the  production  of  sand  for  glass  making  and  other 
purposes,  in  Oregon  Township.  Mineral  resources  are  described  in  detail 
in  Chapter  VI. 

TRANSPORTATION    AND    COMMUNICATION 

The  quadrangle  is  well  served  by  railroads  and  highways.  The  Chi- 
cago and  Northwestern  Railway,  the  Chicago,  Burlington  and  Quincy  Rail- 
road, the  Illinois  Central  Railroad,  the  Lincoln  Highway,  a  state  highway 
along  Rock  River,  and  limestone  macadam  roads  provide  excellent  means 
of  transportation.  The  dirt  roads  are  naturally  good,  since  the  loess-silt 
which  covers  most  of  the  area  is  too  granular  and  pervious  to  form  mud, 
and  too  coherent  to  produce  a  sandy  surface.  A  moderate  amount  of  at- 
tention, including  frequent  dragging,  keeps  these  roads  in  excellent  condi- 
tion. 


CHAPTER  II— GEOLOGIC   TERMS   AND   PRINCIPLES 

This  chapter  has  been  prepared  for  the  non-technical  reader,  and  in- 
troduces the  more  important  conceptions  upon  which  the  rest  of  the  report 
is  based.  In  the  succeeding  chapters,  evidence  is  presented  for  the  inter- 
pretations offered,  but  a  knowledge  of  general  geologic  and  geographic  prin- 
ciples is  assumed.  Detailed  information  on  the  subject  matter  of  the  pres- 
ent chapter  may  be  found  in  any  text-book  of  general  geology. 

Topographic  Map 

The  topographic  map  (Plate  II)  is  one  of  the  series  being  prepared 
by  the  Illinois  State  Geological  Survey  in  cooperation  with  the  United  States 
Geological  Survey.  The  scale  used  is  1  to  62,500 ;  that  is,  one  inch  on  the 
map  represents  62,500  inches  on  the  face  of  the  earth,  or  approximately 
one  mile. 

On  the  map,  the  works  of  man  are  printed  in  black.  Public  roads  are 
indicated  by  double,  continuous  lines ;  for  improved  highways,  one  of  the 
lines  is  heavier;  private  roads  are  indicated  by  double  broken  lines.  Houses 
are  shown  by  small  squares,  and  school  houses  by  the  same  symbol  with  a 
triangular  flag  attached.  Churches  have  a  cross  added  to  the  square  and 
large  buildings  are  mapped  with  their  approximate  shapes.  Where  roads 
do  not  follow  section  lines,  the  latter  are  indicated  by  light  dotted  lines.  A 
series  of  long  dashes  represents  township  boundaries,  and  long  and  short 
dashes,  county  boundaries. 

Surface  forms  are  printed  in  brown.  Elevations  of  many  points  are 
shown  by  brown  numbers,  and  where  these  points  have  been  permanently 
marked  by  a  brass  cap,  set  on  a  pipe  embedded  in  cement,  or  attached  to  a 
building,  a  black  cross  and  the  letters  B  M  (bench  mark)  are  used.  Exact 
elevations  of  these  points  are  given  in  a  government  bulletin1  which  may 
be  obtained  upon  request  to  The  Director,  U.  S.  Geological  Survey,  Wash- 
ington.    Another  paper2  gives  the  exact  geographic  positions  of  many  points. 

Contour  lines  show  the  topography  of  the  area.  A  contour  is  a  line 
passing  through  points  of  equal  elevation,  so  that  a  person  walking  along 
such  a  line  would  walk  on  a  level  and  go  neither  up  nor  down  hill.  The  con- 
tour may  be  considered  as  a  potential  shoreline,  for  if  the  ocean  were  raised 


1  Marshall,    R.    B.,    Spirit   Leveling    in    Illinois    for    the    years    1914-1917,    inclusive, 
U.  S.  Geol.  Survey  Bull.  672,  pp.  31-35,  1918. 

2  Marshall,    R.    B.,    Results    of   triangulation    and    primary    traverse    for    the    years 
1911  and  1912,  U.  S.  Geol.   Survey  Bull.   551,  pp.  135-136,  1914. 

19 


20  DIXON    QUADRANGLE 

800  feet  above  its  present  level,  for  instance,  the  shoreline  would  cross  the 
Dixon  quadrangle  along  the  irregular  course  of  the  800-foot  contour.  On 
the  Dixon  map,  the  contours  are  drawn  at  intervals  of  20  feet,  and  in  pass- 
ing from  one  contour  line  to  another  at  any  place  in  the  area,  one  would 
either  rise  or  descend  20  feet,  regardless  of  the  horizontal  distance.  Where 
the  siope  is  steep,  the  contour  lines  are  close  togther,  and  where  it  is  gentle, 
they  are  far  apart.  Examples  of  steep  slopes  are  shown  along  Rock  River 
and  Franklin  Creek  where  the  contours  are  so  crowded  that  they  almost 
merge.  The  gently  rolling  surface  in  the  southern  third  of  the  area  is  in- 
dicated by  the  very  wide  spacing  of  the  contours. 

Water  features  are  shown  in  blue.  Where  a  stream  flows  throughout 
the  year,  a  solid  line  is  used,  while  intermittent  streams  are  shown 
by  dash-and-double-dot  lines.  Springs  are  represented  by  small  circles, 
usually  at  the  sources  of  streams.  A  large  spring  is  mapped  in  sec.  12,  T. 
22  N.,  R.  10  E.  Marshes  are  shown  by  short  horizontal  lines  with  radiating 
lines  above,  suggesting  tufts  of  grass.  The  only  marsh  indicated  on  the 
map  is  north  of  Kyte  River  in  sec.  11,  T.  23  N.,  R.  10  E. 

Land  Divisions 

Most  of  the  land  west  of  the  Appalachian  Mountains  belonged  at  one 
time  to  the  United  States  Government,  and  was  surveyed  into  townships 
practically  six  miles  square.  If  time  and  funds  had  permitted,  it  would 
have  been  desirable  to  begin  the  surveys  at  the  east  boundaries  of  the  public 
lands  and  carry  them  continuously  wTest  to  the  Pacific.  It  was  necessary, 
however,  to  keep  the  surveys  abreast  of  settlement,  and  as  the  pioneers  did 
not  occupy  the  land  progressively  westward,  but  moved  into  the  more  de- 
sirable areas  first,  surveys  were  initiated  at  many  points.  Whenever  a  new 
survey  was  started,  a  north-south  line  called  a  principal  meridian  was  estab- 
lished and  townships  were  laid  off  to  the  east  and  west  of  it.  From  the 
initial  point  of  the  survey  an  east-west  line,  called  a  base  line,  was  also  run. 
Townships  were  numbered  east  and  west  from  the  principal  meridian  and 
north  and  south  from  the  base  line.  For  example,  the  township  in  which 
most  of  Dixon  is  located  is  Township  21  North,  Range  9  East,  (T.  21  N., 
R.  9  E.),  which  means  that  it  is  the  21st  township  north  of  the  base  line  and 
is  located  in  the  ninth  range  of  townships  east  of  the  principal  meridian. 
The  entire  Dixon  area  was  surveyed  from  the  Fourth  Principal  Meridian 
(Plate  III). 

The  Third  Principal  Meridian  lies  about  four  miles  east  of  the  Dixon 
quadrangle.  Mile  posts  along  this  meridian  are  not  on  the  prolongation  of 
section  lines  surveyed  from  the  Fourth  Meridian,  since  each  survey  started 
from  an  arbitrary  point.  Accordingly,  section  lines  east  and  west  of  the 
Third    Principal    Meridian    do   not    meet   on    that   line   and   east-west    traffic 


GEOLOGIC    PRINCIPLES  21 

must  jog  north  or  south  on  passing  from  the  area  of  one  survey  to  that  of 
the  other. 

The  eastern  and  western  boundaries  of  townships  converge  towards 
the  north  because  all  north-south  lines  become  closer  together  as  they  ap- 
proach the  poles.  In  order  to  keep  the  townships  nearly  six  miles  wide,  it 
is  necessary  to  introduce  correction  lines.  Along  a  correction  line,  the 
southern  boundaries  of  townships  are  made  full  six  miles  in  length.  North- 
south  roads  are  offset  on  correction  lines  in  the  same  way  that  the  Third 
Principal  Meridian  offsets  east- west  roads.  A  correction  line  lies  about 
lj4  miles  north  of  this  area. 

The  township  is  divided  into  36  sections,  practically  a  mile  square,  num- 
bered from  the  northeast  corner  westward  and  alternately  eastward  and 
westward.      (See  Plate  II.) 

General  Geologic  Principles 

ROCKS 

The  rocks  of  the  earth's  surface  may  be  divided  into  three  main  classes : 
igneous,  sedimentary  and  metamorphic. 

Igneous  rocks  are  those  which  have  solidified  from  a  molten  or  paste- 
like condition.  Where  solidification  proceeded  slowly  deep  beneath  the  sur- 
face of  the  earth,  various  minerals  formed,  producing  crystals  of  different 
sizes.  The  various  types  of  crystallized  igneous  rocks,  of  which  granite 
and  diorite  are  the  most  common  examples,  are  distinguished  by  their  tex- 
ture and  their  mineral  components.  Where  the  rock  flowed  out  on  the 
surface  as  a  lava,  it  cooled  much  more  quickly,  forming  very  fine-grained 
or  glassy  rocks.  No  igneous  rocks  are  known  in  place  in  this  quadrangle, 
but  many  igneous  boulders  were  brought  in  by  glaciers. 

Sedimentary  rocks  are  deposited  by  oceans  and  lakes,  running  water, 
winds,  and  glaciers.  These  rocks  consist  principally  of  material  which  has 
been  obtained  from  other  rocks,  and  which  is  deposited  directly  by  these 
agents.  Less  commonly,  various  substances  have  been  extracted  from  the 
water  by  plants  or  animals,  included  in  their  structures,  and  their  organic 
remains  have  accumulated  on  their  death  and  decay. 

Most  sedimentary  rocks  have  been  deposited  as  gravel,  sand,  clay  or 
lime  muds,  which  on  solidification  have  formed  conglomerate,  sandstone, 
shale  or  limestone.  Less  common  types  of  sediments  are  rock  salt,  coal  and 
gypsum.  In  this  quadrangle,  sandstone,  shale,  limestone  and  dolomite  are 
present.  The  conditions  of  their  formation  are  discussed  under  marine 
deposition. 

Metamorphic  rocks  are  formed  from  igneous  or  sedimentary  rocks,  by 
change  of  form,  composition,  and  crystallization  under  intense  heat,  or  pres- 


22  DIXON    QUADRANGLE 

sure,  or  both.  The  more  common  types  of  metamorphic  rocks  are  marble, 
gneiss,  schist,  and  slate,  none  of  which  is  known  in  place  in  this  area.  There 
are,  however,  metamorphic  boulders  in  the  glacial  drift.  It  is  possible  that 
both  igneous  and  metamorphic  rocks  underlie  the  quadrangle  at  depths 
greater  than  2000  feet  (see  Chapter  III),  but  their  position,  character,  and 
structure  are  entirely  unknown,  and  could  be  determined  only  by  deep  drill- 
ing. 

WEATHERING 

At  or  near  the  surface,  the  breaking  down  of  all  types  of  rocks  is  ef- 
fected by  exposure  to  various  geologic  processes,  collectively  known  as 
weathering.  These  processes  may  be  classified  as  mechanical  weathering, 
or  disintegration,  and  chemical  weathering,  or  decomposition.  Mechanical 
weathering  includes  the  various  processes  that  break  up  the  rock  without 
affecting  its  composition.  These  are  principally  the  freezing  of  water  in 
openings  in  the  rock,  which  pries  its  constituents  apart ;  the  expansion  and 
contraction  of  the  surface  as  the  rock  is  heated  and  cooled  by  daily  or 
seasonal  temperature  changes ;  the  wedge  work  of  growing  plant  roots ;  the 
burrowing  of  animals,  and  attrition  of  material  which  is  blown,  rolled, 
thrown  or  rubbed  against  the  solid  rock.  Chemical  weathering  involves  a 
change  in  the  composition  of  the  rock.  Its  most  common  type  is  solution 
of  certain  rock  constituents.  Other  important  forms  are  oxidation,  notably 
of  iron,  and  the  addition  of  carbon  dioxide  or  water  to  the  original  substances 
of  the  rock.  In  this  quadrangle,  mechanical  weathering  is  commonly  illus- 
trated by  the  spalling  off  of  pieces  of  stone  buildings  and  the  occasional  pry- 
ing apart  of  rocks  by  tree  roots.  Chemical  weathering  has  produced  the 
crumbling  surface  zone  of  several  limestone  outcrops  and  has  changed  the 
loess  and  till  of  the  glacial  deposits  from  their  original  blue-gray  to  the 
present  yellow  or  brown  color. 

EROSION 

Erosion  includes  both  weathering  and  the  removal  of  material  by  wind, 
running  water,  waves  or  glaciers.  In  dry  or  barren  areas,  wind  blows  dust 
and  sand  from  place  to  place,  removing  the  finer  material  and  piling  up  the 
remaining  sand  in  irregular  hills  called  dunes.  Examples  of  such  dunes  are 
discussed  on  p.  79. 

Part  of  the  rain  water  runs  over  the  surface,  carrying  with  it  varying 
amounts  of  clay,  silt  and  sand.  This  is  called  slope  wash,  and  where  vege- 
tation does  not  interfere,  it  may  remove  weathered  rock  very  rapidly.  In 
streams,  the  erosive  power  of  water  is  frequently  greater,  and  not  only  sand 
and  sill  are  carried,  but  pebbles  and  even  boulders  may  be  rolled  along, 
grinding  the  bed  of  the  stream  and  breaking  away  other  fragments,  which 
in  turn  are  rolled,  and  form  tools  for  the  river.  With  the  help  of  these  tools, 
the  streams  deepen  and  widen  their  channels. 


GEOLOGIC   PRINCIPLES  23 

In  regions  where  the  winter's  snow  does  not  entirely  melt  during  the 
summer,  snow  accumulates,  and  under  pressure  forms  ice.  With  further 
accumulation,  the  weight  of  overlying  ice  becomes  too  great  for  the  lower 
portion  to  support,  and  the  ice  spreads  outward  from  the  central  area  where 
it  formed.  Such  moving  ice  bodies  are  called  glaciers,  well-known  examples 
of  which  occur  in  the  Alps  and  in  Glacier  National  Park,  Montana.  In  the 
cold  region  near  the  poles,  glaciers  cover  large  areas  and  are  not  confined 
to  valleys  or  mountain  sides.  In  Greenland,  for  instance,  there  is  a  glacier 
covering  over  400,000  square  miles.  Such  a  glacier  is  called  a  continental- 
glacier.  As  the  ice  moves  over  the  country,  it  erodes  the  surface  vigorously, 
sweeps  away  loose  material,  freezes  to  rock  and  pulls  it  along,  and  grinds 
rock  fragments  in  the  bottom  of  the  ice  against  the  underlying  rock  surface. 
In  this  way,  glaciers  remove  great  quantities  of  both  weathered  and  origi- 
nally solid  rock,  and  often  carry  the  material  long  distances  before  deposit- 
ing it.  The  portions  of  North  America  covered  by  glaciers  during  the  last 
period  of  glaciation  are  indicated  in  fig.  14. 

MARINE    DEPOSITION 

STRATIFICATION 

Nearly  all  of  the  eroded  material  is  again  deposited  to  form  sedimentary 
rocks,  of  which  the  most  common  types  are  those  deposited  in  the  ocean. 
Because  sediments  are  usually  found  in  well-defined  beds  or  strata,  they  are 
often  called  stratified  rocks.  The  strata  are  distinguished  from  one  another 
by  changes  in  kind  of  material,  size  of  grain,  or  color  of  cement.  In  the 
marine  strata,  bedding  planes  are  formed  nearly  parallel  to  the  ocean  floor, 
and  any  change  in  material  represents  a  change  in  oceanic  conditions  at  the 
time  of  deposition.  For  instance,  the  change  from  coarse  to  fine  material 
indicates  either  that  the  waves  or  currents  sweeping  the  ocean  floor  became 
less  vigorous  and  brought  finer  sediment,  or  that  there  was  a  reduction  in 
the  size  of  material  contributed  to  the  ocean  by  streams.  Because  these 
strata  were  deposited  on  a  nearly  flat  floor,  any  variation  from  the  hori- 
zontal indicates  that  the  rocks  have  been  deformed ;  consequently,  the  struc- 
ture of  a  region  can  be  determined  from  the  attitude  of  its  beds.  In  any 
such  studies,  however,  only  originally  flat-lying  sediments  can  be  used.  For 
example,  in  this  area,  the  limestone  strata  were  probably  originally  prac- 
tically horizontal.  In  the  St.  Peter  sandstone,  however,  many  beds  were 
deposited  by  strong  currents  with  sloping  or  curving  surfaces.  Such  beds 
which  lie  at  an  angle  with  the  main,  originally  flat,  strata  are  called  cross 
beds.  Cross-bedding  may  often  be  used  to  determine  the  source  of  mate- 
rial or  the  agent  which  deposited  the  rock,  but  its  attitude  is  deceptive  and  is 
usually  ignored  in  structural  studies. 


24  DIXON    QUADRANGLE 

CLASTICS 

Materials  which  ape  moved  in  solid  form,  as  gravel,  sand  and  clay,  are 
called  elastics.  The  kind  and  size  of  material  indicates  the  conditions  in 
the  ocean  at  the  time  of  deposition.  Sand,  for  instance,  is  evidence  of  mod- 
erately strong  currents  which  spread  out  the  coarse  material.  Where  the 
ocean  floor  is  practically  flat,  the  sand  may  extend  over  hundreds  of  square 
mile-  :  but  where  the  bottom  slopes  steeply,  the  water  may  be  too  deep  near 
the  shore  for  active  wave  or  current  work,  and  accordingly  the  zone  of  sand 
deposition  is  very  limited.  Like  the  sand,  clay  and  silt  are  secured  from 
the  land.  Currents  and  waves  carry  clay  farther  from  the  shore  than  sand. 
and  when  the  bottom  slopes  gradually,  the  clay  is  washed  man}"  miles  out 
to  sea.  On  the  other  hand,  in  deep  salt  water,  clay  is  quickly  precipitated. 
and  is  not  carried  far  from  land  unless  currents  -weep  it  over  the  ocean  floor. 

LIMESTONE 

Animals  live  in  nearly  all  parts  of  the  ocean,  and  after  death  their  shells. 
bones,  and  other  hard  parts  settle  to  the  bottom.  The  accumulation  of  these 
animal  remains  is  slow,  and  if  sand  or  clay  is  being  deposited  rapidly,  the 
animal  material  may  form  an  inconspicuous  portion  of  the  strata  :  on  the 
other  hand,  if  the  ocean  is  clear  and  sand  is  not  supplied  by  rivers  or  shore- 
line erosion,  animal  structures  may  accumulate  close  to  or  even  at  the  shore. 
as  in  the  case  of  coral  reefs.  Most  of  the  animal  structures  consist  of  cal- 
cium carbonate  which  has  been  extracted  from  the  water  in  the  same  way 
that  man  builds  his  own  bone.-  from  the  mineral  content  of  the  water  and 
food  that  he  uses.  A  few  plants  also  extract  calcium  carbonate  from  the 
ocean  and  when  they  die  this  calcium  carbonate  is  contributed  to  the  accu- 
mulating sediments.  If  these  calcareous  organic  remains  settle  in  quiet 
water,  they  may  form  a  mass  in  which  most  of  the  original  structure-  can 
be  recognized:  but  where  the  water  is  shallow,  waves  and  currents  ma}"  roll 
and  grind  the  sediment  to  a  fine  mud.  in  which  few  or  no  original  struc- 
tures can  be  determined.  Such  animal  and  subordinate  plant  deposit-  are 
abundant  in  the  Dixon  area,  and  form  the  limestones  of  the  Prairie  du 
Chien.  Plarteville  and  Galena  formation-.  Because  the}-  usually  have  re- 
sulted from  accumulation  in  clear  water,  any  .-tonus  which  brought  mud 
into  the  ocean  are  represented  by  bedding  plane-,  and  stratification  is  easily 
recognizable. 

dolomite 

If  the  ocean  water  contain-  much  magnesium,  dolomite  may  be  formed 
contemporaneously  with  the  deposition  of  the  mud.  In  such  case,  the  mud 
will  not  suffer  further  change  on  induration,  and  the  dolomite  will  be  dense, 
solid,  and  free  from  solution  cavities  and  channel-.  Dolomite  is  also  often 
formed  by  the  substitution  of  magnesium   for  calcium  after  the  limestone 


GEOLOGIC    PRINCIPLES  25 

has  been  indurated.  This  change  develops  a  porous  rock  which  frequently 
contains  solution  cavities  and  channels.  In  the  process  of  dolomitization, 
most  of  the  original  animal  structures  are  entirely  destroyed. 

CONTINENTAL  DEPOSITION 

EOLIAN   DEPOSITS 

In  many  cases,  the  products  of  erosion  are  deposited  on  the  land,  and 
are  then  called  continental  sediments.  In  this  area,  eolian  or  wind-formed 
deposits  are  represented  by  sand  dunes  and  loess.  A  sand  dune  is  formed 
where  an  obstruction  interferes  with  the  movement  of  sand-laden  wind,  so 
that  its  velocity  is  decreased  and  the  sand  is  dropped.  A  pile  or  drift  is 
formed,  to  which  additional  sand  brought  by  the  wind  is  added.  Wind  blow- 
ing up  the  windward  side  of  the  dune  rolls  or  carries  sand  to  the  top.  Some 
of  this  sand  falls  down  onto  the  leeward  side,  causing  that  side  of  the  hill 
to  travel  forward  gradually,  and  perhaps  to  override  and  bury  the  obstacle 
which  originally  caused  its  formation.  Such  moving  sand-hills  are  called 
live  dunes;  those  covered  with  vegetation  are  said  to  be  dead.  Dunes  may 
be  killed  by  planting,  or  by  building  obstructions,  such  as  fences,  on  their 
windward  slopes  to  prevent  the  movement  of  sand.  A  dead  dune  in  sec. 
33,  T.  21  N.,  R.  10  E.,  has  been  revived  by  over-pasturing,  which  has  des- 
troyed the  vegetation  and  removed  the  hindrances  to  wind  activity. 

Loess  is  a  fine  silt  which  has  been  deposited  by  wind  over  all  the  upland 
of  this  area.  It  probably  was  blown  from  areas  of  glacial  till  soon  after 
deposition,  and  from  the  flood-plains  of  streams  flowing  from  those  areas. 
The  material  consists  of  fine-grained  rock  fragments  and  minerals,  such  as 
can  be  found  in  the  glacial  till  of  this  and  the  adjacent  areas.  Where  fresh, 
it  contains  much  original  limestone  material.  Weathering  removes  this  cal- 
careous matter,  and  the  loess  then  is  said  to  be  leached.  One  criterion  of 
the  age  of  a  loess  is  the  amount  of  oxidation  and  leaching  which  it  has  under- 
gone. 

STREAM  DEPOSITS 

Where  tributaries  bring  more  material  to  the  main  stream  than  it  can 
carry,  the  excess  load  is  deposited  on  the  valley  floor.  Similarly,  where  a 
stream  gradient  decreases  sharply,  the  carrying  power  diminishes  and  much 
sediment  may  be  deposited.  Slope  wash  and  tributaries  have  overloaded 
many  streams  in  this  area  and  produced  nearly  flat  bottom  lands  or  Hood- 
plains  along  the  streams.  In  time  of  high  water,  the  stream  often  covers 
this  flood-plain,  and  because  it  flows  there  more  slowly  than  in  the  main 
channel,  it  deposits  additional  alluvium,  building  up  its  flood-plain  still 
higher. 


26  DTXOX    QUADRANGLE 

In  the  same  way.  streams  flowing  from  g-laciers  commonly  cariw  great 
quantities  of  sand  and  gravel,  much  of  which  is  deposited  in  their  channels, 
unless  the  gradient  continues  as  high  as  that  which  the  stream  had  on  leav- 
ing the  ice-sheet.  If  the  stream  deposits  this  sediment,  it  raises  its  channel, 
and,  shifting  back  and  forth  across  the  valley,  may  till  it  to  a  great  depth. 
Deposition  continues  until  the  gradient  of  the  stream  is  sufficient  to  give  it 
the  velocity  required  to  carry  all  the  material  supplied  by  the  melting  ice. 
Such  an  accumulation  of  sand  and  gravel  is  called  a  valley  train.  In  this 
area,  valley  trains  fill  the  Rock  and  Kyte  River  valleys.  Ever  since  the  dep- 
osition of  the  valley  train.  Rock  River  has  been  removing  this  material  bv 
erosion,  producing  the  terraces  described  on  p.  16  (fig.  1).  Other  types 
of  river  deposits  are  unimportant  in  this  area. 

LAKE    DEPOSITS 

In  large  lakes,  sediments  similar  in  many  respects  to  those  of  the  ocean 
are  formed.  In  this  area,  however,  no  lakes  of  importance  are  known  ever 
to  have  existed,  and  lake  deposits  are  confined  to  the  accumulations  of  plant 
material  in  swampy  areas  along  Kyte  River,  Franklin  Creek,  and  a  few  low 
areas  on  the  upland.  In  these  places,  the  contribution  of  streams  has  been 
unimportant,  and  the  work  of  the  wind  negligible.  Rushes  and  cat-tails 
have  deposited  great  masses  of  vegetable  fiber,  and  have  entirely  filled  the 
swamps  with  soft  muck  or  peat.  Accumulation  is  still  going  on  and  the 
material  is  not  yet  solid  enough  to  bear  the  weight  of  a  man.  These  muck 
deposits  are  very  small-scale  examples  of  certain  conditions  typical  of  coal- 
forming  swamps.  Coal  beds  are  the  result  of  accumulation  in  clear  water 
of  plant  material  which  later  formed  peat,  and  being  buried  by  other  sedi- 
ments, was  metamorphosed  to  coal  with  great  loss  of  water  and  gases. 
None  of  the  muck  in  this  area  ever  could  make  satisfactory  coal,  however, 
because  the  streams  have  brought  much  silt  to  the  accumulating  sediment, 
and  this  silt  would  constitute  too  high  a  percentage  of  ash  in  any  coal  that 
might  result. 

GLACIAL  DEPOSITS 

The  material  which  glaciers  erode  from  the  overridden  areas  is  de- 
posited in  part  beneath  the  glacier,  and  in  part  at  its  margin,  where  the  rate 
of  melting  balances  the  rate  of  advance  of  the  ice.  At  such  a  place  the  edge 
of  the  ice  is  standing  still,  although  all  of  the  ice  is  advancing  and  its  trans- 
ported material  accumulates  in  irregular  ridges,  called  terminal  moraines. 
The  material  deposited  beneath  the  glacier  and  during  the  rapid  retreat  of 
its  margin  is  the  (/round  moraine.  Its  composition  is  similar  lo  that  ot  the 
terminal  moraine,  but  prominent  topographic  features  arc  not  produced. 
Ground  moraine  covers   most  of   the   upland  areas  in  the  quadrangle,  and 


GEOLOGIC    PRINCIPLES  27 

while  it  has  been  eroded  from  many  valleys,  it  occurs  on  the  side  slopes 
and  in  the  bottoms  of  others. 

ESKERS 

Where  streams  flow  over  the  surface  of  glaciers  or  follow  channels 
through  or  under  the  ice,  they  frequently  form  a  deposit  of  sand  and  gravel, 
in  every  way  analogous  to  the  valley  trains  of  streams  that  leave  the  glacier. 
If  the  ice-sheet  melts  away  without  further  movement,  these  sand  and  gravel 
accumulations  will  be  left  on  the  surface  of  the  underlying  rock  or  till,  and 
may  form  large,  often  fairly  well-bedded  bodies  of  sand  and  gravel  called 
eskcrs.  During  the  melting  of  the  Illinoian  ice-sheet,  such  an  esker  was  de- 
posited in  this  area  from  Nachusa  to  a  point  a  mile  southwest  of  Grand 
Detour. 

DRIFT 

All  of  the  material  moved  by  a  glacier  is  included  under  the  general 
name  of  drift.  The  unstratified,  unwashed,  unsorted  portion  of  the  drift 
that  accumulates  in  masses  of  heterogeneous  material  in  ground  and  terminal 
moraines  is  called  till.  Till  may  consist  of  any  and  every  kind  of  rock  over 
which  the  ice  has  traveled,  with  the  exception  of  extremely  soluble  types, 
such  as  rock  salt.  Large  boulders,  coarse  gravel,  fine  sand  and  finely 
crushed  rock,  often  called  rock  flour,  are  all  indiscriminately  mingled  in  till. 

CONSOLIDATION    OF    SEDIMENTS 

When  marine  sediments  have  been  deposited,  the  weight  of  the  over- 
lying material  compacts  the  beds  beneath  and  consolidates  the  mud  to  hard 
clay  or  shale.  The  lime  muds  are  similarly  compressed  and  their  particles 
often  adhere,  making  solid  rock.  Similarly,  the  sand  grains  under  pressure 
are  brought  into  close  contact  and  may  form  rock  because  of  pressure  alone. 
Water  in  the  rock  dissolves  mineral  matter,  especially  from  the  points  where 
individual  grains  are  in  contact,  and  deposits  it  between  the  grains  to  form 
a  cement.  In  limestone,  the  cement  is  normally  the  calcium  carbonate  of 
the  rock.  In  sandstone,  calcium  carbonate  or  iron  oxide  is  commonly  in- 
troduced and  serves  as  a  cement ;  or  silica,  of  which,  the  rock  principally 
consists,  is  dissolved  and  precipitated  to  form  a  more  or  less  hard  sandstone. 
In  this  area,  the  sandstones  have  been  only  very  slightly  cemented  and  in 
most  cases  will  crumble  between  one's  fingers.  The  limestones  are  well- 
consolidated  and  the  green  clay  of  the  Glenwood  type  has  formed  a  low- 
grade  shale.  Among  the  glacial  deposits  little  cementation  has  occurred, 
but  in  a  few  places  some  gravel  has  been  thoroughly  consolidated.  In  the 
NW.  J/[  sec.  29,  T.  22  N.,  R.  9  E.,  a  small  body  of  glacial  gravel  has  been 
bound  together  by  calcium  carbonate  to  form  a  weak  conglomerate.  In 
none  of  the  commercial  gravel  pits  is  the  material  so  consolidated  or 
cemented  that  it  cannot  readily  be  removed  with  a  shovel. 


28  DIXOX    QUADRANGLE 


GROUND   WATER 


Water  which  reaches  the  earth  in  the  form  of  rain  or  snow  either  runs 
away  to  join  the  streams  and  so  becomes  part  of  the  run-off,  soaks  into  the 
ground  and  becomes  part  of  the  run-in,  or  evaporates  from  the  surface  into 
the  air  once  more.  The  water  which  runs  in  is  called  "ground  water".  It 
travels  in  a  generally  downward  direction  until  it  reaches  a  surface  beneath 
which  the  rock  is  saturated  with  water.  This  surface  which  separates  the 
saturated  from  the  unsaturated  rocks  above  is  called  the  ground-water  table. 
The  water  beneath  the  ground-water  table  obeys  the  same  laws  as  surface 
water,  flows  down  slopes,  and  reappears  at  the  surface  in  seepages,  springs 
and  artificial  openings  such  as  wells.  The  surface  of  a  river  or  pond  marks 
the  elevation  of  the  ground-water  table.  The  rock  underneath  must  be 
saturated  or  else  the  water  would  seep  away  from  the  pond  or  stream  and 
leave  a  dry  surface.  The  economic  importance  of  the  ground  water  is  dis- 
cussed in  Chapter  VI. 

HISTORICAL    GEOLOGY 

GEOLOGIC   TIME   TABLE 

The  geologic  history  of  the  earth  is  divided  into  live  main  eras  which  in 
turn  consist  of  two  to  seven  periods.  In  general,  each  period  embraces  the 
interval  between  two  important,  wide-spread  changes  in  life  or  in  land-and- 
sea  relations  on  the  earth's  surface.  Periods  are  often  divided  into  cpoclis 
and  these  into  stages.  The  smaller  units  are  recognizable  only  over  limited 
areas,  in  most  cases,  although  some  are  distinctly  marked  over  much  of  the 
earth.  The  sediments  formed  during  a  period  constitute  a  system,  and 
those  of  an  epoch  form  a  series.  In  general,  continuous  beds  of  one  type  of 
rock  or  repeatedly  alternating  beds  of  two  or  more  rocks  are  called  a  for- 
mation. A  table  of  the  geologic  periods,  epochs  and  formations  or  stages 
referred  to  in  this  report  is  given  on  p.  33. 

CORRELATION 

Formations  of  one  area  may  be  proved  to  be  the  same  in  age  as  those 
of  another  region.  The  determination  of  the  age  equivalence  is  called 
correlation.  Various  methods  are  available  for  correlation,  of  which  the 
most  important  are  continuity  of  the  formations,  identical  lithologic  char- 
acter of  one  or  several  beds  or  formations,  fossil  content,  or  similar  relations 
to  some  definitely  datable  event  in  geologic  history. 

Because  of  the  depth  of  glacial  till  over  this  and  surrounding  areas, 
the  formations  here  cannot  be  correlated  by  tracing  them  to  points  where 
they  were  first  described.  Also  with  two  possible  exceptions,  they  are  cov- 
ered by  younger  beds  so  that  they  could  not  be  traced  to  the  type  outcrops 
even    if   there   were   no   glacial    deposits.     Correlation   by   lithology    is   very 


GEOLOGIC    PRINCIPLES  29 

unsatisfactory,  because  the  minerals  of  sedimentary  rocks  have  come  largely 
from  pre-existing  formations,  and  those  from  a  common  source  may  be 
present  in  two  or  more  formations  in  the  same  area.  A  good  example  of 
this  fact  is  offered  by  the  outcrop  of  "New  Richmond"  sandstone  in  Frank- 
lin Creek  valley.  The  sand  grains  in  this  rock  are  scarcely  distinguishable 
from  those  of  the  St.  Peter  formation  above  or  the  Croixan  beneath,  and  it 
is  probable  that  all  the  sand  came  from  the  same  source  in  central  Wiscon- 
sin or  Canada.  The  formations  cannot  be  distinguished  definitely  by  dif- 
ferences in  their  constituents.  It  was  this  practically  identical  lithology 
that  led  James  Shaw  in  his  reconnaissance  of  the  area  fifty  years  ago  to  re- 
gard the  "New  Richmond"  sandstone  as  the  St.  Peter,  and  accordingly  to 
correlate  the  overlying  Shakopee  with  the  Platteville  limestone  which  over- 
lies the  St.  Peter.  In  this  case,  it  is  possible  by  carefully  following  the  out- 
crops, to  show  that  the  St.  Peter  formation  of  Rock  Valley  is  continuous 
with  a  thin  sandstone  overlying  the  Shakopee,  which  Shaw  had  correlated 
with  the  Platteville.  Similarly,  a  careful  study  of  the  lithology  of  the  two 
limestones  indicates  that  their  correlation  is  an  error,  even  though  the  two 
sandstones  cannot  be  distinguished  with  certainty. 

The  evidence  from  historical  geology  in  different  areas  is  difficult  to 
secure,  and  usually  involves  a  large  amount  of  uncertainty  as  to  the  exact 
equivalence  of  the  formations.  No  correlations  in  this  report  are  made 
on  such  a  basis. 

Fossils  are  evidences  of  life  contained  in  the  rocks.  Such  life  traces 
may  be  portions  of  the  animals  or  plants  themselves,  as  shell  or  bone  frag- 
ments, impressions,  molds  or  casts  of  organic  matter,  material  which  has 
replaced  the  original  substance  but  retained  its  structure,  such  as  petrified 
wood,  trails  and  footprints  of  animals,  or  even  structures  made  by  them,  as 
the  worm-borings  in  the  St.  Peter  sandstone  of  this  area.  Paleontology  is 
the  study  and  interpretation  of  these  fossils. 

Paleontologic  evidence  is  the  most  valuable  means  of  correlation,  for 
the  development  of  life  throughout  geologic  time  can  be  traced  in  the  fossil 
record.  Plaving  determined  the  interval  during  which  a  given  form  existed, 
it  is  evident  that  any  formation  containing  this  fossil  must  have  been  de- 
posited between  the  earliest  and  latest  times  when  the  creature  lived.  Free- 
swimming  animals  with  distinctive  hard  parts  are  most  useful,  for  their 
remains  will  be  wide-spread  and  will  make  correlations  possible  over  long- 
distances, 

In  correlating  glacial  deposits,  the  problem  is  rendered  very  difficult  by 
the  mode  of  their  formation.  Contemporaneous  life  is  rarely  buried  in  the 
till,  and  forms  distinctive  of  the  various  glacial  invasions  are  not  known. 
Correlations  are  based  largely  upon  the  length  of  time  the  material  has  been 
exposed  to  weathering  and  erosion.     So,    for   instance,   over   two   areas   of 


30  DIXOX    QUADRANGLE 

till  equally  distant  from  the  main  drainage  line  of  the  region,  the  presump- 
tion is  that  the  one  which  has  suffered  most  erosion  is  the  older.  This  pre- 
sumption must  be  verified  very  carefully,  however,  for  changes  in  original 
topography,  variation  in  climate  and  in  interference  by  bed  rock  with  drain- 
age development,  and  differences  in  original  character  of  material  may  all 
affect  the  result.  One  must  also  be  certain  that  no  later  deposits  have 
covered  either  of  the  areas  which  are  to  be  compared.  Similarly,  where 
erosion  of  the  surface  has  not  occurred,  the  depth  to  which  percolating 
ground  water  has  leached  and  oxidized  the  material  often  gives  strong  evi- 
dence of  the  length  of  exposure  and  of  the  age  of  the  deposits  in  question. 
It  must  be  remembered  that  the  depth  of  oxidation  varies  with  the  amount 
of  material  to  be  oxidized.  If  the  rate  of  oxidation  is  the  same,  a  till 
which  contains  four  per  cent  of  ferrous  iron  will  require  twice  as  much  time 
for  oxidation  to  a  depth  of  one  foot  as  would  a  similar  till  containing  only 
two  per  cent. 

It  is  obvious  that  the  same  condition  affects  the  depth  of  leaching  of 
limestone  material.  If  the  porosity  of  the  till  is  not  the  same,  the  less  porous 
material  retains  the  ground  water  longer  and  so  favors  more  rapid  leaching, 
unless  the  porosity  is  so  very  low  that  the  water  cannot  readily  travel  through 
the  material.  In  that  case,  a  much  smaller  amount  of  water  may  pass  a 
given  point  and  so  the  amount  of  leaching  may  be  much  less  than  in  more 
porous  substances.  Other  things  being  equal,  the  liner  the  material,  the  more 
rapidly  it  will  be  weathered,  for  the  smaller  particles  have  more  surface  ex- 
posed per  unit  of  volume.  The  line  grain  of  the  loess  has  undoubtedly 
favored  deeper  leaching  and  oxidation  than  that  produced  in  gravel  in  the 
same  length  of  time.  In  such  studies,  one  must  be  certain  that  the  leached 
material  has  been  continuously  above  the  ground- water  table,  for  the 
weathering  processes  go  on  very  slowly  in  the  presence  of  the  standing 
water.  Any  error  in  assuming  uninterrupted  weathering  will  vitiate  the 
conclusions  drawn  from  the  field  evidence.  Within  a  small  area,  differences 
in  climate,  such  as  rainfall,  temperature,  amount  of  wind,  season,  and  rate 
of  precipitation  will  not  be  appreciable  ordinarily,  but  they  must  be  con- 
sidered carefully  where  the  distance  between  formations  to  be  correlated  is 
great. 

PHYSIOGRAPHIC  CYCLE 

The  tendency  of  practically  all  processes  of  weathering  and  erosion  is 
to  lower  the  land  surfaces  and  to  till  the  ocean  basins.  In  particular,  streams 
remove  the  soil  and  rock  from  regions  through  which  the)'  tlow.  Given  time 
enough,  they  will  reduce  their  drainage  basins  practically  to  sea  level.  The 
proportion  of  the  work  accomplished  in  a  given  region  is  indicated  by  de- 
scribing the  area  as  young,  mat  it  re  or  old.     A  young  region  has  had  little 


GEOLOGIC   PRINCIPLES 


of  its  upland  dissected  and  removed  by  stream  development.  It  frequently 
contains  lakes  and  swamps  on  its  surface,  due  to  poor  drainage.  In  matu- 
rity, the  upland  is  all  drained  and  largely  removed,  flood-plains  have  devel- 
oped, and  the  relief,  or  difference  in  elevation  between  uplands  and  valley 
floors,  is  the  greatest  of  any  time  in  the  cycle.  In  an  old  region,  the  valley 
sides  slope  gently,  the  hills  are  low  and  rolling,  and  the  drainage  of  the  flood- 
plains  is  poor.  If  erosion  continues,  the  region  becomes  nearly  flat  as  the 
hills  are  removed.  This  flat  or  very  gently  rolling  surface  is  called  a  pene- 
plain, and  the  series  of  topographic  changes  through  which  a  region  passes 
during  erosion  from  youth  to  old  age  and  peneplanation  is  known  as  the 
physiographic  cycle. 

Similarly,  a  young  stream  has  accomplished  little  of  its  ultimate  work. 
It  is  cutting  its  valley  deeper,  developing  tributaries  and  destroying  lakes 
and  falls.  In  maturity,  the  stream  has  stopped  its  rapid  downward  erosion, 
has  developed  a  flood-plain  and  is  maintaining  a  balance  between  material 
supplied  by  tributaries  and  material  removed  by  the  main  stream.  In  old 
age,  the  stream  is  no  longer  vigorously  eroding,  but  carries  most  of  its  load 
in  solution,  has  become  sluggish,  and  meanders  widely  on  its  flood-plain. 

The  Dixon  area  was  reduced  to  a  peneplain  in  the  period  before  glaci- 
ation.  It  was  later  uplifted  and  the  rejuvenated  streams  dissected  the  flat 
surface  until  it  was  perhaps  midway  between  extreme  youth  and  maturity, 
or  in  the  stage  called  late  youth.      (See  fig.  13.) 


CHAPTER  III— STRATIGRAPHY 

The  following  table  lists  the  geologic  groups,  systems,  series  and  rock 
formations   to   which   reference   is   made   in   this   report.     A  graphic  repre- 


FEET 
800  - 


-Q 


U 


r_r 


n: 


T^T 


II,  ii 


iii    i 


r.i.i    i 


ii.  i.i 


k   I     ,  I      ? 


I       !■=»  I        I    ol 


0-15        Loess 

20 


150+      Galena  dolomite 


Platteville 


Lowell  Park 


Blue 


Buff 
-o-7        Glenwood  "shale 

30-180    St  Peter  sandstone 

35-110   Shakopee  dolomite 

0-32       New  Richmond  sandstone 

160         Oneota  dolomite 


L480+    Croixan 


Fig.  2.    Geologic  column  for  Dixon    quadrangle. 

sentation  of  the   formations  outcropping  in   the  quadrangle  is  given  in  the 
geologic  column,  fig.  2. 

32 


GEOLOGIC   TIME   TABLE 


33 


Table  1. — Geologic  Formations 


Group 


System 


Cenozoic 


Mesozoic 


Paleozoic 


Recent 


Pleistocene 


Tertiary  (sub- 
group) 
Cretaceous 
C  Permian 
Pennsylvanian 
Mississippian 
Devonian 

Silurian 


Ordovician 


Series 

Wisconsin    (glacial) 

Late  Wisconsin 

Early  Wisconsin 
Peorian    (interglacial) 
Iowan   (glacial) 
Sangamon    (interglacial) 
Illinoian    (glacial) 
Yarmouth    (interglacial) 
Kansan    (glacial) 
Aftonian    (interglacial) 
Nebraskan    (glacial) 


Formation 


Cambrian 


Proterozoic 
Archeozoic 


f  Niagaran 

I  Alexandrian 
Upper  Ordovician 


Middle   Ordovician 


Lower  Ordovician  or 
Prairie  du  Chien 


Upper  Cambrian  or 
Croixan    (Potsdam) 


'  Keweenawan 
Upper  Huronian 
Middle  Huronian 
Lower  Huronian 


Niagaran  limestone 


Maquoketa  shales 
Galena  dolomite 
Platteville  limestone 

Lowell  Park 

Blue 

Buff 
Glenwood  shale 
St.   Peter   sandstone 
Shakopee  dolomite 
New  Richmond  sandstone 
Oneota  dolomite 
Jordan    sandstone 
Trempealeau  formation 
Mazomanie   sandstone 
Pranconia  formation 
Dresbach  formation 
Eau  Claire  formation 
Mt.   Simon  formation 


34  DIXON    QUADRANGLE 

Pre-Cambrian  Rocks 
CRYSTALLINES 

The  oldest  rock  outcropping  in  this  State  is  of  Lower  Ordovician  age  and 
is  exposed  in  this  quadrangle  along  Franklin  Creek.  Knowledge  of  pre- 
Cambrian  and  Cambrian  formations  in  Illinois  is  obtained  entirely  from 
well  records  and  from  outcrops  and  drillings  in  adjacent  states. 

In  northern  and  central  Wisconsin,  a  complex  series  of  pre-Cambrian 
igneous  and  metamorphic  rocks  crops  out.  At  the  close  of  the  pre-Cambrian 
a  fairly  well-developed  peneplain  beveled  these  formations.  This  peneplain 
was  preserved  by  burial  under  the  heavy  sandstones  of  Croixan  (Upper 
Cambrian)  age,  and  has  been  traced  southward  beneath  these  sandstones  in 
numerous  wells  in  southern  Wisconsin.  Presumably  the  pre-Cambrian 
complex  and  its  peneplain  continue  into  northern  Illinois  and  underlie  this 
quadrangle.  These  crystalline  rocks  have  not,  however,  been  penetrated  by 
any  well  in  this  state,  and  their  character  and  distribution  are  unknown. 

Weidman 1  has  prepared  a  structure-contour  map  of  this  peneplain 
surface  in  Wisconsin,  which,  projected  into  northern  Illinois,  indicates  that 
at  Dixon  the  pre-Cambrian  crystalline  rocks  should  be  found  about  700  feet 
below  sea  level.  The  Dixon  Water  Company's  deepest  well,  however,  pene- 
trated 1203  feet  below  sea  level  without  encountering  crystalline  rock,  and 
three  other  wells  in  Dixon  Township  were  drilled  more  than  1000  feet  below 
sea  level  without  finding  either  igneous  or  metamorphic  rock.  The  bottom 
of  the  Amboy  city  well,  1600  feet  below  sea  level,  is  in  sandstone.  Evi- 
dently the  southward  dip  of  the  peneplained  crystalline  surface  is  consider- 
ably steeper  than  has  been  previously  recognized.  The  depth  of  the  crys- 
talline rocks,  as  well  as  their  character,  is  uncertain.  Available  evidence 
indicates  only  that  they  lie  more  than  1200  feet  below  sea  level  and  are 
buried  under  more  than  1800  feet  of  Paleozoic  sediments  throughout  this 
quadrangle. 

KEWEENAWAN    (?)     SANDSTONE 

Keweenawan  red  sandstone  underlies  the  Croixan  sandstones  in  north- 
western Wisconsin  and  eastern  Minnesota.2  Several  wells  in  northern  Illi- 
nois have  penetrated  a  red  sandstone  which  Thwaites3  suggests  may  be 
Keweenawan,  beneath  lighter-colored,  typical  Croixan  sandstones. 


1  Weidman,  S.,  and  Schultz,  A.  R.,  Water  supplies  of  Wisconsin:  Wisconsin 
Geol.    and   Nat.    Hist.    Survey   Bull.    35,    PL   I,    1915. 

2  Hall,  C.  W.,  Meinzer,  O.  E.,  and  Fuller,  M.  L.,  Geology  and  underground  waters 
of  southeastern  Minnesota:  U.  S.  Geol.  Survey  Water-Supply  Paper  256,  pp.  32,  48, 
1911. 

Thwaites,  F.  T.,  Sandstones  of  the  Wisconsin  coast  of  Lake  Superior:  Wiscon- 
sin  Geol.   and  Nat.   Hist.   Survey  Bull.    25,   pp.    58-61,    1912. 

:|  Thwaites,  F.  T.,  Paleozoic  rocks  in  deep  wells  in  "Wisconsin  and  northern 
Illinois:    Jour.    Geol.,    vol.    31,    p.    555,    1923. 


I'RE-CAMBRIAN    ROCKS  35 

In  this  quadrangle,  knowledge  of  Cambrian  and  possible  pre-Cambrian 
formations  is  obtained  from  three  well  logs.  The  Dixon  Water  Company 
has  four  wells  near  its  pumping  station  in  the  southwest  corner  of  sec.  33, 
T.  22  N.,  R.  9  E.  These  wells  are  1610,  1720,  1765  and  1860  feet  deep, 
respectively,  but  only  the  log  of  the  1765-foot  well  is  available  (p.  37). 
No  samples  of  drill  cuttings  were  saved.  Two  wells  have  been  drilled  on 
the  Dixon  Epileptic  Colony  farm  near  the  southwest  corner  of  sec.  21,  T. 
22  N.,  R.  9  E.  Samples  from  these  wells  were  saved  and  studied  for  the 
State  Geological  Survey  by  C.  B.  Anderson,  whose  identifications  are  shown 
in  the  log  on  p.  38. 

At  Amboy,  three  miles  south  of  this  quadrangle,  the  2220-foot  city 
water  well  was  drilled  to  1600  feet  below  sea  level.  Although  the  surface 
elevation  is  about  160  feet  lower  than  at  the  Dixon  Colony,  the  well  started 
about  100  feet  higher  stratigraphically  in  the  Galena  dolomite,  and  accord- 
ingly penetrated  only  about  200  feet  of  strata  lower  than  those  in  the  Dixon 
Colony  well  No.  1.  No  written  log  of  this  well  is  available,  but  it  is  re- 
ported that  the  bottom  of  the  well  was  in  a  distinctly  pink,  but  not  red, 
sand.4  Water  of  good  quality  and  abundant  quantity  has  been  obtained 
from  all  these  wells.  Dissolved  matter  is  moderate  and  suspended  matter 
or  sediment  is  negligible. 

Thwaites5  made  the  tentative  suggestion  that  the  lower  76  feet  of  the 
Colony  No.  2  well  may  be  Keweenawan.  If  this  is  so,  the  lower  218  feet 
of  the  adjacent  well  No.  1  must  also  be  Keweenawan.  Assuming  the  dis- 
tance from  the  top  of  the  St.  Peter  to  the  Keweenawan  as  the  same  in  all 
wells  in  this  region,  the  lower  100  feet  of  the  deepest  Dixon  city  well  and 
the  bottom  418  feet  of  the  Amboy  well  would  be  in  Keweenawan  sediments. 
This  assumption  cannot  be  proved,  however,  in  the  absence  of  carefully  kept 
drill  records  and  of  identifiable  horizon  markers. 

Descriptions  of  the  Keweenawan  sandstones6  have  emphasized  the  large 
amount  of  shale  interbedded  with  the  sandstones,  the  dark  red  color  rarely 
varied  by  pink  or  white  beds,  and  the  brackish  or  saline  character  of  the 
water.  It  is  notable  that  none  of  these  characteristics  are  found  in  the 
possible  Keweenawan  beds  of  this  area.  In  the  deep  Colony  well  No.  1, 
there  are  only  21  per  cent  of  red  sandstone  and  4  per  cent  of  shale  in  this 
doubtful  zone;  in  No.  2  there  is  20  per  cent  of  red  sandstone  and  no  shale; 
and  the  Amboy  well  is  stated  to  have  found  clean  pink  sand,  similar  to  the 
overlying  Mt.  Simon.  In  none  of  the  wells  is  the  water  noticeably  brackish. 
Correlation  based  on  lithology  is  notoriously  dangerous,  but  since  it  is  upon 

4  Jonas    Stultz,    driller,    Amboy. 

5  Thwaites,   F.    T.,    Paleozoic   rocks   in    deep   wells    in   Wisconsin   and    northern    Tlli- 
nois:      Jour.   Geol.,    vol.    31,   p.    534,   fig.    1,    1923. 

6  Hall,  C.  W.,  et  al,  op.  cit. 

Thwaites,   F.  T.,  Wisconsin  Geol.  and  Nat.   Hist.   Survey  Bull.   25,   pp.   58-61,    1912. 


36  DIXON    QUADRANGLE 

this  very  basis  that  the  Keweenawan  age  is  suggested,  the  use  of  lithologic 
evidence  seems  justified  in  the  present  instance.  There  is  a  possibility  that 
the  deep  wells  penetrated  the  Keweenawan,  but  the  additional  evidence  here 
presented  makes  this  seem  very  doubtful.  The  writer  considers  the  bottoms 
of  all  the  wells  as  Cambrian.  How  much  deeper  the  Keweenawan  sand- 
stone, if  present,  and  the  pre-Cambrian  crystallines  lie,  must  remain  a  matter 
of  conjecture  until  more  drilling  has  been  done. 

Paleozoic  Group 

CAMBRIAN    SYSTEM 
CROIXAN    SERIES 

Upper  Cambrian  formations  of  the  upper  Mississippi  valley  were  origi- 
nally grouped  together  as  the  Potsdam  formation,  thus  correlating  them  with 
the  Upper  Cambrian  rocks  of  Potsdam,  New  York.  Because  further  study 
proved  that  the  two  series  were  not  of  identical  age,  Winchell7  in  1873  pro- 
posed the  name  "St.  Croixan"  for  the  formations  typically  developed  along 
St.  Croix  River  on  the  Minnesota-  Wisconsin  boundary.  The  term 
"Croixan"  is  now  used  by  the  Illinois  State  Geological  Survey.  The  near- 
est outcrop  of  the  Croixan  series  is  approximately  42  miles  northeast  of 
this  quadrangle,  near  Beloit,  Wisconsin.  Within  the  quadrangle,  the 
Croixan  has  been  penetrated  by  the  four  city  water  wells  at  Dixon,  the  two 
wells  at  Dixon  Epileptic  Colony,  and  by  a  well  near  Honey  Creek,  which 
was  sunk  more  than  TOO  feet  in  search  for  oil.  The  logs  of  three  of  the  Dixon 
Water  Company  wells  and  of  the  oil-test  well  are  not  available.  Possibly 
a  log  published  in  1890  of  a  "deep  well  near  Dixon,  Illinois,"  8  represents 
the  first  well  drilled  for  the  company.  The  record  shows  only  10  changes 
in  rock  penetrated;  depths  are  stated  in  round  numbers,  and  the  total  depth 
as  published  is  30  feet  greater  than  that  shown  on  the  company's  books. 
The  formations  can  be  correlated  only  in  the  most  general  terms,  and  the 
log  is  not  considered  reliable. 

The  log  of  the  1765-foot  well  which  follows  on  page  37  was  furnished 
by  the  company.     Formation  names   have  been  supplied  by  the  writer. 


7  Winchell,    N.    H.,    General    sketch  of    the    geology   of   Minnesota:    Geol.    and   Nat. 
Hist.    Survey    of   Minnesota    First   Ann.  Rept.    1873,    pp.    7-72. 

8  Tiffany,    A.    S.,    Record    of   a   deep  well   near   Dixon,    Illinois:    Amer.    Geol.,    vol.    5, 
p.   124,   1890. 


CAMBRIAN    SYSTEM  Si 

Driller's   log  of  well  of  the  Dixon  Water  Company,  in   the   SW.  corner  sec.  S3, 

T.  22  N.,  R.  9  E. 

Elevation— 657  feet 
Description  of  strata  Thickness      Depth 

Feet  Feet 

Surficial  material    9  9 

Platteville 

Limestone    95  104 

Glenwood  and  St.  Peter  (glauconitic) 

Shale,   sandy    56  160 

St.  Peter 

Sand   rock    178  338 

Prairie  du  Chien 
Shakopee 

Marl,   red    71  409 

Oneota 

Limestone     114  523 

Croixan 

Marl,   red    17  540 

Lime   rock 172  712 

Shale,  blue  94  806 

Sand  rock  183  989 

Shale,  blue  131  1120 

Sand  rock  645  1765 

It  is  unfortunate  that  accurate  samples  from  every  10  feet  of  drilling- 
are  not  available  for  study.  Because  of  the  importance  to  people  who  are 
about  to  drill  for  water,  coal,  oil,  or  other  purposes,  the  Illinois  State  Geo- 
logical Survey  is  endeavoring  to  secure  and  preserve  samples  from  all  im- 
portant drill  holes.  Those  who  are  doing  drilling  may  obtain  sample  bags, 
and  instructions  for  taking  samples,  free  upon  request  to  the  Survey.  A 
detailed  log  based  on  the  examination  will  be  furnished  whenever  desired. 
Much  unnecessary  drilling  can  be  avoided  by  having  on  file  an  adequate 
collection  of  such  drill  records. 

In  drilling  the  Dixon  Epileptic  Colony  well  No.  2,  samples  of  cuttings 
were  taken  at  frequent  intervals  and  the  resulting  log  shows  by  contrast 
with  that  of  the  Dixon  Water  Company  the  value  of  such  samples.  Only 
the  Cambrian  portion  of  the  log  is  presented  here.  The  correlations  with 
the  Wisconsin  section  are  those  of  Thwaites9  except  that  76  feet  of  doubt- 
ful Keweenawan  rocks  have  been  included  by  the  writer  in  the  Mt.  Simon 
formation. 


9  Thwaites,   F.   T.,   Paleozoic   rocks   in   deep   wells   in   Wisconsin   and   northern   Illi- 
nois:   Jour.    Geol.,   vol.    31,    p.    534,    fig.    1,    1923. 


38 


DIXON    QUADRANGLE 


Partial  log  of  Dixon  Epileptic  Colony  well  No.  2,  in  the  SW.  %  sec.  21,  T. 

R.  9  E. 


N., 


Elevation — 780  feet 


Formation 

Prairie  du  Chien 

Oneota    dolomite    

Cambrian 

C'roixan    series 

Jordan  sandstone 

Trempealeau    formation 

Franconia  formation 

Dresbach  formation 
Eau  Claire   formation 

Mt.    Simon   formation 


Description  of  strata 


Thickness      Depth 
Feet  Feet 


Sandstone,  sandy  dolomite, 
siliceous  oolite,  and  dark 
red   shale    18  460 

Dolomite,  gray,  fine-grained 
to  sub-crystalline ;  practi- 
cally no  sand   or  shale...         184  644 

Dolomite,  slightly  sandy, 
greenish-gray,  with  glau- 
conite    grains    80  724 

Sandstone,  colorless,  well- 
rounded  grains   145  869 

Dolomitic  sandstone,  shale, 
gray,  and  dolomite,  gray 
to  buff   211  1080 

Sandstone,  various  colors 
but  chiefly  white,  pink 
and  gray;  fine  to  very 
coarse-grained     700  1780 


This  well  extended  to  a  depth  of  only  1780  feet,  but  well  No.  1,  situated 
near  No.  2,  reached  a  depth  of  1922  feet.  The  following  entries  are  from 
the  log  of  well  No.  1 : 

Thickness      Depth 
Feet  Feet 

Sand  and  shale,  chocolate-color 8  1783 

Sand,  pinkish-gray,  in  clean,  large  and  medium  grains 42  1825 

Sand,    reddish,    medium    to    coarse-grained 46  1871 

Sand,  gray-pink,  large  and  mediun.  grains 51  1922 

The  above  log  is  generalized  from  the  original  record,  which  describes 
148  samples.  The  detailed  log  is  on  file  in  the  State  Geological  Survey 
offices,  and  is  available  to  anyone  who  wishes  to  study  it. 

The  correlations  are  based  entirely  upon  lithology  since  no  fossils  were 
obtained  in  any  drill  cuttings  collected.  Formations  have  been  traced  with 
some  degree  of  certainty  from  the  outcrop  in  Wisconsin  through  various 
wells  to  Dixon.     Thwaites10  has  presented  in  some  detail  the  evidence  sup- 


()i>.  cit. 


ORDOVICIAN    SYSTEM  39 

porting  the  correlations,  and  since  no  new  data  are  available,  the  reference 
of  these  beds  to  their  respective  formations  need  not  be  discussed  further. 
The  thickness  of  the  Croixan  series  is  here  more  than  1480  feet,  which 
is  greater  than  any  previously  recorded  in  Illinois.  Probably  it  was  pene- 
trated 200  feet  farther  in  the  Amboy  well,  but  a  satisfactory  record  is  not 
available.  Since  the  bottom  of  the  Croixan  is  not  known  in  Illinois,  there 
is  no  means  of  determining  its  total  thickness. 

ORDOVICIAN  SYSTEM 

All  the  indurated  rocks  which  outcrop  in  this  area  are  of  Ordovician 
age,  in  the  usual  sense  of  the  term.  Ulrich11  and  others  have  assigned  the 
lower  member  of  the  Prairie  du  Chien,  the  Oneota  dolomite,  to  the  Canadian 
system,  and  the  two  upper  members  to  the  Ozarkian.  These  systems  have 
not  been  recognized  by  this  Survey  and  the  entire  formation  is  here  treated 
as  Ordovician. 

THE  PRAIRIE  DU   CHIEN   SERIES 

In  the  earliest  geologic  reports  on  the  upper  Mississippi  valley,  the  dom- 
inantly  magnesian  limestone  series  between  the  Croixan  and  the  St.  Peter 
formations  was  called  the  Lower  Magnesian12  and  the  rocks  from  the  Galena 
to  the  Niagaran,  inclusive,  were  named  the  Upper  Magnesian.  Finding  of 
the  thick,  calcareous  Maquoketa  shales  in  this  series  led  to  the  early  drop- 
ping of  Upper  Magnesian  as  a  formation  name.  Lower  Magnesian  re- 
mained in  common  use  until  recently,  because  it  described  an  outstanding 
characteristic  of  the  formation.  Grant  and  Burchard13  in  1907  proposed 
Prairie  du  Chien  as  a  geographic  name  for  the  series,  which  is  well  exposed 
in  the  Mississippi  River  bluffs  near  Prairie  du  Chien,  Wis. 

Bain14  proposed  the  division  of  the  series  into  the  Oneota  dolomite 
below,  the  New  Richmond  sandstone,  and  the  Shakopee  dolomite  above. 

ONEOTA    DOLOMITE 

Name.  The  lowest  member  of  the  Prairie  du  Chien  was  named  Oneota 
by  McGee15  from  Oneota  (now  called  Upper  Iowa)  River  which  enters 
Mississippi  River  near  the  northeastern  corner  of  Iowa. 


11  Ulrich,  E.  O.,  Revision  of  the  Paleozoic  systems:  Bull.  Geol.  Soc.  Amer.,  vol.  22, 
pi.  27,   1911. 

12  Owen,   David   Dale,   Ex.   Doc.    239,    26th   Cong.,    1st   sess.,    p.    17,    1S40. 

"Grant,  U.  S.,  and  Burchard,  E.  P.,  U.  S.  Geol.  Survey  Geol.  Atlas,  Lancaster- 
Mineral  Point  folio  (No.  145),  p.  3,  1907.  Bain  used  Prairie  du  Chien  in  190G  (U.  S. 
Geol.  Survey  Bull.  294,  p.  18,  1906),  citing  the  manuscript  of  the  Lancaster-Mineral 
Point    folio   as    proposing   the    name. 

14  Bain,  H.  F.,  Zinc  and  lead  deposits  of  northwestern  Illinois:  U.  S.  Geo!  Survey 
Bull.    246,  p.    17,    1905. 

15  McGee,  W.  J.,  Pleistocene  history  of  northeastern  Iowa:  U.  S.  Geol.  Survey 
Eleventh  Ann.  Rept.,  pt.   1,  p.   331,   1891. 


■iO  DIXON    QUADRANGLE 

LitJwIogy.  At  its  outcrops,  the  Oneota  dolomite  is  commonly  described 
as  a  thin  to  thick-bedded,  roughly  stratified  magnesian  limestone,  contain- 
ing considerable  amounts  of  clay,  both  in  shaly  layers  and  intimately  inter- 
mingled m  the  limestone,  with  very  subordinate  amounts  of  chert,  sand,  and 
crystalline  quartz. 

In  this  quadrangle,  the  Oneota  dolomite  is  known  only  by  well  records. 
Cuttings  from  the  Dixon  Epileptic  Colony  well  Xo.  '2  show  a  predominantly 
gray  to  pink,  subcrystalline  to  crystalline  dolomite.  White  chert  is  com- 
mon, pink  or  yellow  chert  is  less  common,  and  sand  grains  are  rare.  In 
55  samples,  shale  was  noted  only  twice.  In  several  of  the  lower  bed-,  geodes 
lined  with  quartz  crystals  were  found.  This  rock  extended  from  294  feet 
below  the  surface  to  d<30  feet  below,  making  a  thickness  of  166  feet.  The 
normal  thickness  of  the  Oneota  formation  reported  in  northeastern  Iowa  is 
£00  to  350  feet.  At  the  nearest  outcrops  in  Wisconsin,  the  thickness  was 
reduced  by  erosion  before  St.  Peter  deposition  to  less  than  100  feet. 

A  real  distribution.  The  Oneota  dolomite  probably  underlies  the  entire 
quadrangle.  Where  the  rock  crops  out  in  Wisconsin,  Iowa  and  Minnesota, 
it  is  usually  described  as  conformable  with  the  underlying  Cambrian.  Its 
uniformity,  its  freedom  from  sand  and  shale,  and  its  regular  appearance  in 
deep  wells  throughout  northern  Illinois  suggest  that  it  was  deposited  over 
the  Dixon  quadrangle  with  a  thickness  of  more  than  150  feet.  Deep  erosion 
preceded  the  deposition  of  the  St.  Peter,  but  the  top  of  the  sand  was  approxi- 
mately plane  in  this  area.  Its  thickness  here  is  not  known  to  exceed  200 
feet,  although  one  log;  of  doubtful  accuracy  records  340  feet  of  sandstone 
above  55  feet  of  Oneota.  With  an  additional  mantle  of  100  feet  of  Shako- 
pee  and  "New  Richmond",  it  seems  improbable  that  the  Oneota  was  entirely 
removed  at  any  place  before  the  St.  Peter  sand  was  laid  down. 

_  '-elation.  Xo  fossils  were  found  in  the  cuttings  described  above, 
and  the  correlation  oi  this  formation  with  the  Oneota  depends  upon  its 
stratigraphic  position  and  normal  lithologic  character.  The  Prairie  du 
Chien  formation  is  usually  correlated  with  the  Beekmantown  series  of  New 
York.  Ulrich,16  however,  regards  the  Prairie  du  Chien  as  older  than  most 
of  the  Beekmantown.  and  calls  it  Ozarkian.  The  Little  Falls  dolomite  (^Di- 
vision A  and  part  of  B  i  of  the  Beekmantown.  is  correlated  by  him  with  the 
Oneota  and  part  of  the  upper  Croixan  series. 

"NEW    RI<  HMOND"    -AXDSTOXE 

Name.  The  "New  Richmond""  sandstone  member  of  the  Prairie  du 
Chien  formation  was  named  by  Wooster17  at  New  Richmond.  St.  Croix 
County.  Wisconsin. 


16  Ulrich,  E.  O.,  Revision  of  the  Taleozoie  svstems:  Bull.  Geol.  Soc.  Amer., 
VOL    22.    p.    640    and    pi.    27.    1911. 

"Wooster,  L.  C.  Geology  of  the  lower  St.  Croix  district:  Geology  of  Wiscon- 
sin,   vol.    IV.    p. 


NEW    RICHMOND       SANDSTONE 


41 


Lithology.  In  this  quadrangle,  the  "New  Richmond"  is  a  massive, 
poorly  bedded,  slightly  cemented  and  remarkably  pure  quartz  sandstone. 
Fresh  exposures  do  not  show  bedding,  but  weathering  develops  traces  of 
horizontal  beds  and  sweeping  curves  of  cross-bedding  whose  dip  decreases 
from  15°  at  the  top  to  0°  where  the  curve  is  tangent  to  the  main  or  true  bed- 
ding. (Fig.  3.)  The  sand  varies  from  0.03  mm.  to  1  mm.  in  diameter.  Large 
grains  are  beautifully  rounded  and  "frosted";  the  smaller  grains  show  less 
wear  and  some  are  quite  angular.     Aside  from  quartz,  the  rock  contains  a 


Fig.  3.  Bar  cross-bedding  in  the  "New  Richmond" 
sandstone,  SW.  M  sec.  34,  T.  22  N.,  R.  10  E.  The 
exposure  is  about  15  feet  high. 


fraction  of  one  per  cent  of  white  chert  fragments.  These  are  dull,  porous, 
and  thoroughly  weathered.  They  are  sharply  angular,  however,  and  the 
weathering  is  probably  due  to  solution  since  deposition,  as  they  are  now 
too  soft  to  be  transported.  Cement  is  almost  entirely  lacking,  and  hand 
specimens  are  very  difficult  to  obtain  because  of  the  very  "tender"  character 
of  the  rock. 


42  DIXON    gUADKAXGLE 

Topographic  expression.  Being  very  easily  eroded,  but  overlain  by  the 
resistant  Shakopee  dolomite,  the  formation  is  exposed  in  a  box  canyon. 
Lateral  erosion  is  rapidly  pushing  back  the  foot  of  the  canyon  walls,  but 
the  contrasting  resistances  of  the  two  formations  maintain  the  vertical  bluffs. 
In  one  place,  this  canyon  is  deeper  than  its  width. 

Thickness.  At  the  only  recognized  outcrops  in  this  quadrangle,  the 
rock  is  exposed  in  two  places  to  a  height  of  '2d  feet  above  Franklin  Creek. 
Excavations  for  the  abutments  of  the  Lincoln  Highway  bridge  across 
Franklin  Creek  reached  the  Oneota  dolomite  eight  feet  below  water  level, 
giving  a  total  thickness  of  32  feet  for  the  formation  at  that  point.  Idle  for- 
mation is  strictly  homogeneous  and  cannot  be  divided  into  beds  or  zones. 
As  noted  below,  it  is  missing  in  all  available  deep  well  logs. 

A  real  distribution.  This  formation  is  known  to  outcrop  only  in  a  nar- 
row strip  along  Franklin  Creek  in  sec.  2.  T.  21  X..  R.  10  E..  and  in  sees. 
33  and  3d,  T.  22  X..  R.  10  E.  I  See  Plate  I.)  None  of  the  deep-well  logs 
of  the  quadrangle  record  the  sand.  It  is  possible  that  some  of  the  sand- 
stone poorly  exposed  beside  the  Shakopee  outcrops  in  Rock  River  valley 
represents  this  formation.  Xone  of  those  beds  are  clearly  underneath  the 
Shakopee.  and  much  sandstone  is  unmistakably  resting  upon  it.  The  sand 
is  of  nearly  uniform  size,  which  is  characteristic  of  the  St.  Peter  rather 
than  "Xew  Richmond."  The  available  evidence  indicates  St.  Peter  age.  and 
the  exposures  are  so  mapped,  although  the  other  alternative  cannot  be  defi- 
nitely disproved. 

The  known  exposures  probably  represent  a  bar  or  bars  in  the  Prairie 
du  Chien  ocean  because  (1)  all  clay  is  thoroughly  removed  from  the  sand, 
(2)  the  sizes  of  sand  grains  are  too  varied  for  wind  transportation.  (3) 
the  gently  curving  cross-beds  are  not  steep  enough  for  dune  deposits,  (d) 
the  cross-beds  dip  regularly  to  the  west,  and  are  not  interrupted  and  chan- 
neled as  in  river  bars.  I  5  I  the  tops  of  the  cross-beds  are  planed  off  smooth- 
lv  at  three  horizons,  whereas  wind  or  stream  erosion  would  more  probably 
have  left  irregular  surface-,  and  I  6  |  at  each  exposure  the  Shakopee  forms 
a  gentle  anticline  with  beds  parallel  to  the  surface  of  the  sandstone,  as  would 
be  the  case  with  lime  muds  consolidating  and  settling  over  an  incompres- 
sible sand  lens. 

This  interpretation  accords  with  the  absence  of  the  "New  Richmond" 
in  well  logs  in  the  vicinity.  It  is  improbable  that  the  sandstone  ever  covered 
the  area  a-  a  whole. 

rrelation  and  relation  to  adjacent  formations.  No  fossils  have  been 
found  in  the  sandstone.  It  is  here  doubtfully  correlated  with  the  New 
Richmond  of  Wooster18,  Bain13  and  others  on  the  basis  ni  its  stratigraphic 


]»  Wooster,    L.   C,    op.    cit. 

19  Bain.    H.    F..    Zinc    and    lr;;.l    (h-posits    of    Illinois:    U.    S.    Heel.    Survey    Bull.     LMtf, 
p.    iv 


SHAKOPEE   DOLOMITE  43 

position  and  lithological  character.  However,  sandstone  is  found  at  various 
horizons  in  the  Oneota  and  Shakopee.  Upham20  for  instance,  reports  three 
beds  of  sandstone  in  a  65-foot  section  of  the  Shakopee.  Other  geologists 
have  reported  sandstones  at  various  horizons  in  the  Prairie  du  Chien.  The 
shaly  lower  Shakopee  beds  immediately  overlying  this  sand  in  sec.  2  contain 
sands  or  sandstones  at  three  horizons.  One  bed  of  sandstone  is  two  feet 
thick  and  another  dominantly  arenaceous  zone  is  5^  feet  thick.  There  is 
no  evidence  of  a  continuous  sandstone  body  either  in  this  quadrangle  or  in 
the  areas  to  the  northeast.  Southeastward,  in  the  Hennepin  and  La  Salle 
quadrangles,  the  "New  Richmond"  is  a  sheet  sand,  reaching  a  maximum 
thickness  of  188  feet.21  In  southwestern  Wisconsin  and  northeastern  Iowa, 
the  sandstone  is  very  irregular  in  thickness,  but  there  are  usually  one  or 
more  sandstones  in  the  Prairie  du  Chien  series. 

There  is  no  information  about  the  contact  of  this  sand  with  the  under- 
lying Oneota.  It  is  apparently  conformable  with  the  Shakopee  dolomite 
above,  and  is  approximately  equivalent  to  the  type  "New  Richmond,"  but  an 
exact  correlation  cannot  be  made. 

SHAKOPEE  DOLOMITE 

Name  and  lithology.  The  upper  member  of  the  Prairie  du  Chien  was 
named  Shakopee  by  N.  H.  Winchell22  from  the  town  of  that  name  in  Scott 
County,  Minnesota.  While  it  is  predominantly  a  fine-grained,  porous,  buff, 
argillaceous  dolomite,  it  contains  considerable  amounts  of  variously  colored 
shales  and  some  sandstone.  The  typical  dolomite  is  nearly  massive,  but 
weathering  develops  beds  6  to  10  inches  thick.  The  weathered  rock  is  buff, 
light  brown  or  yellow-brown,  but  the  weathered  surface  is  usually  gray  or 
dirty  white.  When  fresh,  the  rock  is  light  buff  or  gray.  Sand  is  abundant 
in  the  lower  beds  and  at  several  horizons  in  the  more  shaly  portions,  but  the 
massive  dolomite  is  nearly  free  from  sand.  Its  weathered  surface  appears 
very  sandy,  due  to  projecting  dolomite  crystals  which  resist  weather  attack 
better  than  the  fine-grained  ground  mass.  The  shales  are  normally  calcitic 
or  dolomitic,  buff  or  yellow,  and  well-laminated.  Red,  purple  and  green 
shales  are  not  uncommon,  however,  and  these  are  usually  free  from  carbon- 
ates. Much  of  the  clay  shale  is  sandy ;  and  sandstone  beds,  up  to  two 
feet  in  thickness,  are  interbedded  with  the  shale.  The  sand  grains,  whether 
in  the  carbonate  or  argillaceous  rock,  are  well-rounded ;  many  are  "frosted" 
and  dulled  by  wind  action.  The  sand  is  identical  in  appearance  with  that 
of  the  "New  Richmond"  below  and  both  probably  came   from  the  same 


20  Upham,  Warren,  Geology  of  Minnesota,  vol.   1,  p.   429,   1884. 

21  Cady,   G.  H.,   Geology   of  the  Hennepin  and  La   Salle   quadrangles:    Illinois   State 
Geol.    Survey  Bull.   37,   p.   34,   1919. 

-Winchell,    N.    H.,    Minnesota    Geol.    and    Nat.    Hist.    Survey    Second    Ann.    Rept., 
p.    138,    1873. 


44  DIXON    QUADRANGLE 

source.  White,  yellow  and  a  few  pink  cherts  appear  in  the  more  massive 
layers.  The  cherts  are  lenticular  masses  ranging  up  to  six  inches  in  diam- 
eter; re-entrant  angles  and  depressions  with  quartz-crystal  linings  are  found 
on  some  masses.  These  are  not  geodes  although  they  approach  those  forms. 
Oolitic  chert  is  rare,  but  is  important  since  it  identifies  this  formation  as 
Prairie  du  Chien.23  There  are  also  thin  beds  of  a  peculiar,  stringy  or  ropy, 
coarse-grained  dolomite  which  appears  as  though  the  material  had  been 
worked  over  by  large  earthworms,  and  which  is  called  "wormy"  dolomite  in 
the  absence  of  a  better  term. 

The  shaly  dolomite  is  abundantly  mud-cracked,  marked  with  shallow 
water  ripples,  and  in  many  places  broken  and  crumpled  into  an  edgewise 


Fig.  4.  Typical  exposure,  10  feet  high,  of  Shakopee  dolomite,  sec.  34, 
T.  22  N.,  R.  10  E.  A  mass  of  brecciated  material  with  slightly 
curved,  overlying  beds  is  shown  right  of  the  center  of  the  photo- 
graph. 

conglomerate,  in  which  there  are  cryptozoon  fragments.  The  shaly  beds 
lying  immediately  above  these  brecciated  masses  curve  over  them ;  but  higher 
beds  are  not  deformed.  The  broken  fragments  are  not  weathered  or 
rounded  by  attrition,  and  there  is  no  evidence  of  weathering  or  transporta- 
tion. Possibly  these  peculiar  masses  resulted  from  slumping  on  the  flanks 
of  algal  reefs.     (Fig.  4.) 

28  Thwaites,    F.   T.,    Paleozoic   rocks   in   deep   wells   in   northern   Illinois:    Jour.    Geol., 
vol.    31,    p.    542,    1923. 


SHAKOPEE    DOLOMITE  45 

Topographic  expression,  thickness  and  a/real  distribution.  The  massive 
dolomite  resists  erosion,  and  forms  cliffs  where  streams  are  cutting  then- 
channels  deeper,  as  in  the  Franklin  Creek  box  canyon   (sees.  33  and  34,  T. 

22  N.,  R.  10  E.),  and  along  tributaries  of  Clear  Creek,  near  Tealls  Corners 
(sees.  4  and  9,  T.  22  N.,  R.  10  E.).  Where  the  streams  have  reached  grade, 
valley  sides  are  more  gentle  and  are  covered  with  a  rich  but  stony  soil. 

The  thickest  section  of  the  Shakopee  found  in  this  quadrangle  is  63 
feet,  measured  on  the  west  bluff  of  Rock  River  in  the  SE.  %  sec.  30,  T. 

23  N.,  R.  10  E.  Neither  top  nor  bottom  of  the  member  is  exposed  at  this 
place,  however.  In  the  cuttings  from  Dixon  Colony  well  No.  2,  C.  B.  An- 
derson reports 

"Dolomite,  gray,  subcrystalline,  in  many  cases  containing  embedded  sand 

grains    83  feet 

Dolomite,  chert  and  some  siliceous  oolite 29  feet" 

making  a  total  of  112  feet. 

The  thickest  section  that  can  be  studied  in  detail  is  exposed  in  a  ravine 
on  the  south  side  of  Franklin  Creek.  Although  the  St.  Peter  lies  on  top, 
the  section  represents  only  the  lower  portion  of  the  Shakopee.  More  mas- 
sive beds,  representing  the  upper  Shakopee,  outcrop  near  Tealls  Corners  and 
along  Rock  River. 

Section  of  lower  Shakopee  member,  Prairie  clu  Chien  formation,  in  the  NW.   14 
SW.  %  sec.  S.'i,  T.  22  N.,  R.  10  E. 
Description  of  strata  Thickness 

Ft.        In. 
St.  Peter  sandstone 
Shakopee  member 

Green  clay  and  clay  shale 8 

Buff -brown,    earthy   limestone , 1 

Mottled  buff  and  blue-gray  or  green-gray,  fucoidal  and  "wormy" 
dolomite,  porous  in  many  places,  irregular,  lumpy  beds  2  inches 
or  less  in  thickness,  some  floating  sand  grains  in  lower  beds.  ...       8 

Green,  buff  and  ash-gray,  sandy  shales,  well-laminated 6 

Buff  to  light  brown,  dense,  uniform,  fine-grained  dolomite.  Pew 
mottled,  ripple-marked  and  mud-cracked  irregular  beds  inter- 
calated; base  containing  some  brecciated  dolomite 7  6 

Gray  or  ashen,  laminated  shale  with  thin  sandstone  layers 2 

Buff,  "wormy"  and  fucoidal  dolomite,  alternating  coarse  and  fine- 
grained, weathering  chalk-white,  alternately  even-bedded'  with 
conchoidal   fracture  and   lenticular   beds,   with   granular,   hackly 

fracture,  weathering  with  a  lumpy  surface 3 

Massive,  poorly  bedded  dolomite  with  many  floating  sand  grains 
in  lower  part,  shaly  layers  ripple-marked  and  mud-cracked';  ap- 
proximately         17 

"New  Richmond"  sandstone 

Pure  white,  crumbling  quartz  sandstone 

Total     39  8 


46  DIX0X    QUADRANGLE 

\\  hile  the  above  section  is  fairly  typical,  none  of  these  beds  can  be  identified 
at  a  point  a  mile  upstream,  where,  in  a  12-foot  exposure,  there  is  much  red 
and  purple  shale,  more  dolomitic  shale  and  less  massive  dolomite.  In  this 
exposure,  several  shale  beds  pinch  out  within  a  distance  of  300  feet. 

To  show  the  rapid  horizontal  variation  of  this  formation,  the  following 
section  located  two  miles  upstream  from  the  first  one  is  described. 


Section    or  lower   Shakopee   member.   Prairie   du    Chien    formation,    in    the  SE.   V± 

XW.  y±  sec.  2.  T.  21  N.,  R.  10  E. 
Description  of  strata  Thickness 

Ft.         In. 
St.  Peter  sandstone 
Shakopee  member 

Buff    dolomite,    with    floating    sand   grains    and    thin,    argillaceous 

limestone  layers   lithologically   similar   to   "water   lime" 12 

White.    0.5   mm. -grained   sandstone,   many   beds   with    dolomite   ce- 
ment,  sandy  dolomite,   and  sanely  dolomitic  thin-bedded  shale..       5  6 

Buff  to  gray  dolomite  and  interbedded  ■"water-lime"  layers 3 

"Water  lime'*   shaly  dolomite 6 

White,    saccharoidal    sandstone 8 

"Water  lime"   shaly   dolomite 1 

Buff,    sandy    dolomite    and    "water-lime"    layers    with    small    amount 

of   red    shale 1  6 

White  sandstone  and  dolomitic  sandstone 2 

Sandy   dolomite 6 

Buff,  thin-bedded  "water  lime"  or  "cotton  rock" 1  6 

Crystalline  buff  dolomite,  with  much  floating  sand 2 

"Water   lime"    8 

Green,  gray  and  purple  clay  shales,  interlaminated  and  containing 

a  bed  of  sand  one  inch  thick 3 

"New   Richmond"    sandstone 

Total    Shakopee    member 33  10 

The  distribution  of  the  Shakopee  exposures  follows  in  general  the  axis 
of  the  La  Salle  anticline  across  the  quadrangle.  As  shown  in  Plate  I.  the 
Shakopee  is  discontinuously  exposed  along  Franklin  Creek  from  a  point  two 
miles  southeast  of  Franklin  Grove  to  a  point  four  miles  northeast  of  that 
town.  It  also  outcrops  near  Tealls  Corners  in  Clear  Creek  and  tributary 
valleys,  at  several  places  northward  along  Rock  River  valley,  and  two  miles 
east  of  Lighthouse  Point  in  sec.  30,  T.  23  X..  R.  11  E. 

Paleontologic  character.  Because  of  the  dolomitization  of  the  Shako- 
pee member,  its  fossil  content  has  been  almost  entirely  destroyed.  The  clay 
shales  are  non-fossiliferous  ;  the  dolomitic  shales  originally  contained  numer- 
ous gastropod  shells,  but  none  of  these  is  sufficiently  preserved  to  be  specif- 
ically identifiable.  The  following  fossils  were  collected  from  the  Shakopee 
in  the  Dixon  quadrangle.  Identifications  have  been  checked  by  Dr.  J.  J. 
( rallowav. 


SHAKOPEE   DOLOMITE  47 

Fossils   from   the   Shakopee   member,   Prairie   dn   Chien  formation 

Cryptozoon  minnesotense  Winchell 

Hormotoma  sp. 

Lingulepis  acuminata  Conrad 

Liospira  sp. 

Ophileta  sp. 

Fucoids  are  abundant  in  the  shaly  limestones,  and  the  "wormy"  dolomite  is 
probably  to  be  classed  with  the  other  fucoids. 

Correlation,  The  usual  correlation  of  the  Shakopee  has  been  with  the 
Beekmantown  (lower  Ordovician)  of  New  York.  Ulrich  considers  the 
formation  older  than  most  of  the  Beekmantown  and  puts  it  in  the  upper  part 
of  a  new  system,  the  Ozarkian,  which  he  places  definitely  below  the  Ordo- 
vician. The  presence  of  Lingulepis  acuminata  suggests  a  correlation  with 
the  Hoyt  limestone  of  New  York,  in  which  this  form  is  prominent.  Ulrich 
and  Cushing24  consider  the  Hoyt  distinctly  older  than  most  of  the  Beek- 
mantown, and  place  it  in  the  upper  Ozarkian.  Lacking  more  conclusive 
evidence,  the  writer  adopts  the  usual  correlation  with  the  Beekmantown  and 
does  not  limit  it  to  the  Hoyt  member  alone. 

Relations  to  adjacent  formations.  The  base  of  the  Shakopee  is  entirely 
conformable  with  the  top  of  the  "New  Richmond"  at  the  only  certain  ex- 
posures in  Franklin  Creek.  On  the  other  hand,  a  sharply  marked  erosional 
unconformity  always  separates  the  Prairie  du  Chien  from  the  St.  Peter. 
This  unconformity  is  also  angular  at  several  places  in  Franklin  Creek  valley 
and  in  the  NW.  %  sec.  16  and  the  SW.  ]/A  SE.  yA  sec.  9,  T.  23  N.,  R.  10  E. 
Flat-lying  St.  Peter  lies  on  Shakopee  beds  with  dips  ranging  up  to  45°. 
(NE.  yA  NE.>4  sec.  33,  T.  22  N.,  R.  10  E.)  Erosion  cut  deeply  and  steep- 
ly into  the  Shakopee  before  the  St.  Peter  was  deposited.  At  several  places 
where  the  two  formations  are  horizontal,  the  contact  dips  over  20°.  No 
residual  soil  or  weathered  dolomite  is  found  at  the  contact.  Fragments  of 
fresh,  angular  dolomite  and  even  of  shale  are  found  in  the  St.  Peter  near  the 
steep  contacts.  As  an  example  of  these  relations,  the  hill  west  of  Rock 
River  in  sec.  30,  T.  23  N.,  R.  10  E.,  may  be  cited.  Sandstone  forms  the 
northwest  and  south  sides  of  the  hill,  but  dolomite  makes  the  extreme  top 
and  part  of  the  east  face.  The  total  height  of  the  buried  hill  is  unknown  ; 
but  dolomite  and  sandstone  exposures  prove  a  minimum  of  63  feet.  The 
contact  is  largely  hidden,  but  outcrops  show  that  its  dip  is  more  than  18° 
and  less  than  27°.  Fragments  of  dolomite  are  found  in  the  sandstone  near 
the  Shakopee,  but  they  are  entirely  missing  at  a  distance  of  200  feet.  The  low- 
est dolomite  is  exposed  10  feet  above  the  river.  Sandstone  forms  the  bank 
75  feet  north.     It  is  possible  that  this  sandstone  is  "New  Richmond,"  under- 


24 Ulrich,   E.   O.,   and   Cushing,   H.   P.,    Age   and   relations   of   the    Little   Falls   dolo- 
mite: New  York  State  Mus.  Bull.  140,  pp.  130-136,  1010. 


48  DIXOX    QUADRANGLE 

lying  the  dolomite,  but  there  is  no  evidence  for  this  suggestion.  If  it  is  St. 
Peter,  the  Shakopee  hill  was  more  than  7  5  feet  high.  Similar  relations  but 
showing  less  erosion  are  observable  at  all  Prairie  du  Chien  outcrops  except 
in  Franklin  Creek,  where  the  St.  Peter  rests  upon  and  appears  conform- 
able to  beds  of  lower  Shakopee.  Half  a  mile  north,  the  maximum  angular 
unconformity  and  sharp  erosion  are  found.  Obviously,  the  apparent  con- 
formity results  merely  from  parallel  bedding  on  both  sides  of  a  flat  erosion 
surface. 

MIDDLE    ORDOVICIAN    SERIES 
ST.    PETER    SAXDSTOXE 

Name.  This  formation  was  originally  defined  by  D.  D.  Owen25  and 
was  named  from  St.  Peter's  (now  called  Minnesota)  River,  near  St. 
Paul,  Minnesota.     It  does  not  occur  near  the  town  of  St.  Peter. 

LitJiologic  character.  This  well-known  formation  has  its  usual  char- 
acteristics in  this  region.  It  is  a  white,  medium-grained,  poorly  cemented, 
thick-bedded,  pure  quartz  sandstone.  Its  color  is  strikingly  white,  except  at 
a  few  places  where  it  is  stained  brown  by  ferric  oxide  or  green  with  a  glau- 
conitic  clay.  Its  grains  are  uniformly  well-rounded  quartz  sand,  varying 
from  0.2  mm.  to  1.0  mm.  in  diameter.  The  sand  is  better  sorted,  more 
rounded  and  more  uniformly  worn  by  eolian  transportation  than  are  the 
grains  in  the  "New  Richmond''  sandstone.  Some  of  the  sand  has  been 
enlarged  by  a  secondary  growth  of  quartz.  These  grains  glisten  as  light  is 
reflected  from  their  perfect  crystal  faces,  and  contrast  sharply  with  the  usual 
dull  or  milk-white  appearance  of  the  "frosted"  sand.  Cement  is  so  nearly 
absent  that  it  is  commonly  difficult  to  collect  a  specimen  of  the  rock,  and  its 
crumbling  character  permits  rapid  erosion  wherever  the  rock  is  exposed  to 
friction.  In  spite  of  its  softness,  the  rock  does  not  weather  rapidly.  (Figs. 
5  and  6.)  Bedding  is  usually  evident  on  a  large  exposure,  but  is  never 
striking,  and  may  be  difficult  to  recognize  on  small  surfaces.  The  strata 
range  from  six  inches  to  three  feet  in  thickness  and  are  more  prominent 
where  the  rock  is  weathered.  Bedding  is  marked  by  change  in  size  of  grain, 
rather  than  by  change  in  color  or  character  of  material.  Most  of  the  bed- 
ding is  normal,  but  cross-bedding  appears  at  many  places.  The  cross-beds 
have  the  long,  sweeping  curves  of  the  standing- water  type,  and  are  not  at 
all  suggestive  of  wind  or  stream  deposits.  In  no  case  do  the  cross-beds  dip 
at  an  angle  exceeding  18°  ;  eolian  strata  commonly  have  dips  of  2T°  to  32°. 

The  sand  is  here,  as  throughout  the  Mississippi  Valley,  a  pure  quartz 
sand.  Most  analyses  of  samples  from  this  quadrangle  show  more  than  98 
per  cent  silica,  and  some  have  been  reported  with  over  99  per  cent.  The 
most  common  impurity  is  iron  in  the  form  of  limonite.  This  is  disseminated 
through  the  rock  in  a  few  places,  giving  it  a  faint  yellowish  tint,  but  is  more 


25  Owen,    D.   D.,    Sen.    Exec.    Doc.    No.    2,    30th    Cong.    1st    sess.,    p.    16i».    IS  17. 


ST.    PETER    SANDSTONE 


49 


often  deposited  between  the  grains  along  joint  planes,  and  less  often  along 
bedding  planes.  Along  these  channels,  it  cements  the  rock  for  thicknesses 
of  one  to  four  inches  into  a  hard,  heavy,  dark-brown  sandstone.  Weather- 
ing removes  the  softer  sandstone,  and  leaves  the  iron-cemented  sandstone 
projecting  as  dark  ribs  from  the  general  white  surface.     At  present,  water 


Fig.  5.    Weathered  bluff  of  St.  Peter  sandstone,  showing  etching  by 
wind  and  frost  action  along  softer  beds  and  some  joint  planes. 


Fig.  6.  Bluff  of  St.  Peter  sandstone,  east  of  Green  Rock,  SE.  corner, 
NW.  14  sec.  11,  T.  22  N.,  R.  10  E.  The  highest  sandstone  exposed 
is  about  85  feet  above  river  level. 


in  the  sandstone  does  not  contain  iron,  for  exposures  remain  white,  and  iron 
is  not  deposited  by  springs  coming  from  the  St.  Peter. 

Next  to  iron,  the  most  common  impurity  is  a  glauconitic  green  clay 
which  coats  the  sand  grains  and  fills  the  spaces  between  them.  Hand  speci- 
mens appear  to  be  green  sand,  but  the  clay  coating  can  readily  be  removed. 


50  DIXON    QUADRANGLE 

One  analysis  showed  that  the  clay  constituted  about  5  per  cent  of  the  rock 
and  that  the  potash  content  of  the  specimen  was  .22  per  cent.  This  is  4.4 
per  cent  of  the  coating,  or  nearly  the  theoretical  potash  content  of  glauconite. 
Prolonged  boiling  with  hydrochloric  acid  does  not  destroy  the  green  color 
nor  extract  the  iron  content.  The  color,  potash  content,  insolubility  of  the 
iron,  and  coating  relation  are  normal  for  non-foraminiferal  glauconite,  such 
as  is  sometimes  deposited  in  shallow  water.  The  best  exposure  of  this  green 
sand  is  at  "Green  Rock,"  a  cliff  a  mile  northwest  of  Grand  Detour,  where 
the  upper  22  feet  of  the  St.  Peter  consists  of  this  sand.  Although  the  green 
sand  is  found  at  various  horizons  throughout  the  formation,  it  is  most  abun- 
dant near  the  top. 

Topographic  expression.  Because  of  its  softness,  streams  easily  erode 
the  St.  Peter  to  grade  and  then  by  lateral  planation  widen  the  valleys  and 
develop  the  flood-plains.  Where  the  stream  is  widening  the  valley,  the  sides 
are  steep.  This  is  especially  the  case  where  the  overlying  Platteville  lime- 
stone protects  the  top  of  the  slope.  Typical  box  canyons  result,  with  flat 
floors  and  vertical  sides.  Where  the  limestone  is  missing,  after  the  stream 
reaches  grade  the  valley  sides  become  more  gentle,  and  the  divides  between 
the  streams  are  slowly  reduced  to  rounded,  sandy  hills.  Vertical  exposures 
are  slowly  destroyed  by  wearing  off  the  top  of  the  cliff  and  by  talus  burying 
its  foot.     Weathering  of  faces  protected  from  friction  is  very  slow. 

Thickness  and  areal  distribution.  Measured  thicknesses  of  this  forma- 
tion vary  from  30  to  180  feet.  A  direct  measurement  cannot  be  made  at 
any  point  in  the  area,  except  in  a  well,  but  both  the  maximum  and  minimum 
measurements  are  taken  where  the  St.  Peter  is  apparently  horizontal  and  the 
distance  from  Platteville  to  Shakopee  outcrops  is  less  than  a  quarter  of  a 
mile.  The  formation  is  thinnest  in  the  NW.  ]/A  sec.  27,  T.  22  N.,  R.  10  E., 
and  its  greatest  thickness  is  south  of  Devils  Backbone  in  Oregon  Township. 
Along  Rock  River  from  the  northern  boundary  of  the  quadrangle  to  a  point 
a  mile  west  of  Grand  Detour,  the  thickness  is  certainly  over  100  feet,  except 
where  Shakopee  dolomite  hills  extend  up  into  the  St.  Peter  formation;  and 
from  sec.  17  to  sec.  30,  T.  23  N.,  R.  10  E.,  the  sandstone  is  normally  over 
160  feet  thick.  Yet  in  section  30,  on  top  of  the  Shakopee  hill  referred  to 
on  page  47,  the  thickness  cannot  have  exceeded  80  feet.  In  each  case  of 
estimated  thickness,  the  base  of  the  section  is  the  top  or  side  of  a  Shakopee 
dolomite  hill.  The  dolomite  is  not  sufficiently  exposed  to  permit  an  estimate 
of  its  average  relief,  but  hills  over  60  feet  high  are  known  on  the  Shakopee 
surface.  Two  well  logs  are  available,  but  both  are  unreliable.  Each  reports 
about  50  feet  of  shale  from  the  Glenwood  horizon ;  yet  at  no  exposure  in  the 
quadrangle  or  adjacent  areas  is  this  shale  over  8  feet  thick.  Possibly  it 
caved  and  contaminated  the  cuttings  in  the  Dixon  Water  Company's  well 
(p.  37).       Although   the   Colony   well    records    the   shale    as    50    feet   be- 


ST.    PETER    SANDSTONE  51 

neath  the  surface,  from  excavations  near  the  well  and  sections  measured 
half  a  mile  northeast,  it  is  known  that  the  shale  is  at  least  95  feet  beneath 
the  surface.  The  Water  Company's  well  record  shows  175  feet  of  St.  Peter, 
and  the  Colony  well,  82  feet.  Probably  the  average  thickness  over  the  en- 
tire area  is  about  160  feet,  although  this  estimate  is  believed  to  be  too  small 
rather  than  too  large. 

The  best  continuous  exposure  in  the  area  is  at  Green  Rock  (fig.  6) 
where  83  feet  of  normal  sandstone  is  overlain  by  22  feet  of  green  sand 
with  minor  amounts  of  interbedded  white  sand.  In  the  lower  83  feet,  no 
distinction  could  be  made  between  beds,  a  description  of  any  one  bed  being 
applicable  to  any  other.  This  section  shows  much  more  green  sand  than 
is  normal.  On  the  whole,  the  green  sand  probably  does  not  constitute  4 
per  cent  of  the  formation. 

The  St.  Peter  covers  the  entire  quadrangle  except  for  the  limited  areas 
of  Prairie  du  Chien  outcrop.  The  sandstone  is  the  surface  formation  over 
most  of  the  La  Salle  anticline,  and  therefore  outcrops  in  a  broad  belt  ex- 
tending from  the  southeastern  corner  of  the  area  to  the  center  of  the  north- 
ern boundary.  In  addition,  it  occurs  along  Rock  River  almost  to  Dixon  and 
occupies  most  of  the  northeastern  portion  of  the  quadrangle.  (Plates  I 
and  V.)  It  is  best  exposed  along  the  larger  streams  where  erosion  is  con- 
tinually uncovering  fresh  surfaces. 

Paleontologic  character  and  correlation.  The  only  fossil  found  in  the 
formation  in  this  area  is  a  worm  boring,  Scolithns  minncsotensis  Hall.  This 
was  found  about  65  feet  below  the  top  of  the  formation  at  the  south  end 
of  the  Rock  River  bridge  at  Grand  Detour,  and  also  about  10  feet  from 
the  top  of  the  sandstone  in  the  NE.  ]/A  sec.  26,  T.  23  N.,  R.  10  E.  Shells 
were  probably  buried  in  the  sand  as  it  was  deposited,  but  the  formation  is  so 
porous  that  freely  circulating  water  could  easily  dissolve  the  calcareous 
matter  completely.  The  loose,  unconsolidated  sand  could  not  preserve  casts 
of  the  shells  and  no  trace  of  them  was  left.  Marine  fossils  have  been  found 
by  Winchell,26  Sardeson,27  and  Trowbridge. 2S  On  the  basis  of  these  fossils 
and  its  stratigraphic  position,  the  formation  is  usually  correlated  with  the 
upper  Chazy  series  of  the  Ordovician. 

Relations  to  adjacent  formations.  As  already  described,  the  St. 
Peter-Shakopee  contact  is  an  erosional  unconformity  of  marked  relief.  The 
St.  Peter-Glenwood  contact  is  gradational,  for  the  lower  Glenwood  is  very 
sandy ;  but  sand  is  not  abundant  more  than  two  feet  above  the  contact.    The 


26  Winchell,  N.  H.,  Minnesota  Geol.  and  Nat.  Hist.  Survey  Fourth  Ann.  Rept., 
p.    41,    1875. 

37  Sardeson,  F.  W.,  Fossils  in  the  St.  Peter:  Minnesota  Soc.  Nat.  Sci.  Bull.,  vol. 
4,    pp.    64-87,    1896. 

2S  Trowbridge,  A.  C,  Origin  of  the  St.  Peter  sandstone:  Iowa  Acad.  Sci.  Proa, 
vol.   24,   p.    173,    1917. 


52  DIXON    QUADRANGLE 

surface  of  the  St.  Peter  was  nearly  plain  when  the  Glenwood  was  deposited, 
The  most  conspicuous  exception  is  a  mound  of  sandstone,  rising  about  20 
feet  above  the  general  level  of  the  St.  Peter,  and  offsetting  the  St.  Peter- 
Glenwood  boundary  nearly  half  a  mile  in  sees.  22  and  23,  T.  22  N.,  R.  10  E. 
The  top  of  the  St.  Peter  was  also  probably  higher  than  the  general  plain  in 
the  neighborhood  of  Devils  Backbone,  Oregon  Township,  for  the  Glenwood 
is  very  thin  and  locally  absent,  while  the  basal  Platteville  is  10  to  15  feet 
thinner  than  usual. 

GLENWOOD     SHALE 

Name  and  character.  A  gray-green  to  olive-green  sandy  shale  over- 
lying the  St.  Peter  has  been  named  Glenwood29  at  its  outcrop  in  Glenwood 
Township,  near  Decorah,  la.  Occurrence  of  a  green  shale  above  the  St. 
Peter  has  commonly  been  reported,  but  it  is  normally  thin  and  generally 
has  been  regarded  as  the  lowest  bed  of  the  Platteville,  or  less  often  as  the 
top  of  the  St.  Peter.  In  this  area,  however,  the  shale  is  different  from  any 
part  of  either  adjacent  formation30 ;  it  is  conspicuous  at  several  localities ; 
it  causes  practically  all  the  springs  of  the  area,  and  its  economic  possibili- 
ties are  so  interesting  that  it  is  separately  described. 

The  Glenwood  is  intermediate  between  clay  and  shale,  is  characteristic- 
ally sandy  in  its  lower  beds,  and  is  even  an  argillaceous  sand  in  some  places. 
The  clay  is  soft,  greasy,  plastic  and  adherent  when  wet.  Where  fresh,  it 
is  grass  green,  but  on  exposure,  it  slowly  fades  and  becomes  gray  or  buff 
and  finally  weathers  to  a  dark  brown.  Its  potash  content  is  high.  Possible 
utilization  of  the  Glenwood  is  discussed  in  Chapter  VI. 

Topographic  expression.  Because  of  its  soft  character,  the  tendency 
of  the  overlying  limestone  to  slide  on  the  greasy  clay  and  the  great  amount 
of  glacial  drift  in  the  area,  outcrops  are  rare,  being  limited  to  bluff  faces  or 
rock-bedded  ravines.  Presence  of  the  shale  is  indicated  on  many  hillsides 
by  springs  which  occur  along  the  outcrop.  Water  seeping  through  the  lime- 
stone follows  the  surface  of  the  impervious  Glenwood  and  appears  in  springs 
and  seepages,  often  high  on  a  hillside.  Being  less  resistant  to  erosion  than 
the  St.  Peter,  the  shale  with  the  sandstone  forms  a  cliff  under  a  protecting 
limestone  cap. 

Thickness.  Where  normally  developed,  the  shale  varied  from  2^  to 
7  feet  in  thickness.  Part  of  this  variation  may  be  due  to  slumping  down 
of  overlying  limestone,  but  drillers  report  similar  irregularities  in  wells.  In 
general,  the  lower  portion  of  the  shale  is  quite  sandy,  in  places  being  an 
argillaceous  sand.     The  sandy  zone  is  limited  to  the  lower  two  feet,  above 


29  Calvin,  S.,  Geology  of  Winneshiek  County:  Iowa  Geol.  Survey,  vol.  XVI,  p.  61, 
1906. 

:!0  Bevan,  Arthur,  The  Glenwood  beds  as  a  horizon  marker  at  the  base  of  the 
Platteville  formation:  Illinois  State  Geol.  Survey  Report  of  Investigations  No.  9, 
1926,  is  interesting  in  this  connection. 


GLENWOOD    SHALE PLATTEVILLE    LIMESTONE  53 

which  the  clay  is  quite  uniform  in  its  freedom  from  sand,  even  lamination, 
and  regular  grass  to  olive-green  color.  The  shale  is  thin  or  entirely  miss- 
ing on  the  crest  of  the  La  Salle  anticline  and  reaches  its  maximum  thickness 
along  the  west  flank  of  that  structure.  The  amount  of  shale  varies  with 
the  original  depth  of  clay  deposited,  rather  than  being  affected  by  later 
erosion,  and  since  the  top  of  the  St.  Peter  was  nearly  a  plane  surface,  the 
Glen  wood  thickness  varies  only  slightly  over  limited  areas.  Excellent  ex- 
posures of  the  shale  may  be  found  in  ravines  entering  Rock  River  between 
Pine  Creek  and  the  Sandusky  Cement  plant  at  Dixon,  but  the  best  exposures 
are  north  of  the  Dixon-Grand  Detour  road  in  sees.  15  and  22  and  on  the 
south  side  of  sec.  22,  T.  22  N.,  R.  9  E. 

Areal  extent.  The  shale  outcrops  between  the  Platteville  and  St.  Peter 
formations  along  both  sides  of  Rock  River  from  the  cement  plant  to  Grand 
Detour  and  along  the  west  side  of  the  river  northward  to  the  Chicago,  Bur- 
lington and  Quincy  Railroad  in  Oregon  Township.  Similar  outcrops  follow 
both  sides  of  Pine  Creek  valley,  beyond  the  northern  edge  of  the  quadrangle. 
The  shale  is  not  well  known  in  the  eastern  and  south  central  parts  of  the 
area,  in  part  because  of  the  heavy  mantle  of  glacial  till,  but  also  because 
apparently  it  was  not  deposited  continuously  over  the  axis  of  the  La  Salle 
anticline. 

Age,  correlations  and  relations.  No  fossils  have  been  found  in  this 
shale,  but  it  is  correlated  on  the  basis  of  its  position  and  lithology  with  the 
Glenwood  and  other  green  shales  known  between  the  St.  Peter  and  the 
Platteville.  For  the  same  reasons,  it  is  correlated  with  the  Joachim  lime- 
stone of  Missouri.  It  marks  a  complete  change  in  sedimentary  conditions, 
and  usually  is  regarded  as  the  first  of  the  Platteville  deposits.  The  shale 
appears  conformable  with  both  the  St.  Peter  and  the  Platteville,  and  seems 
to  indicate  a  change  in  sediment  brought  to  the  ocean  rather  than  a  dias- 
trophic  event. 

PLATTEVILLE    LIMESTONE 

Name.  The  Platteville  limestone  was  named  by  Bain31  from  the  town 
of  Platteville,  Wisconsin,  where  the  formation  is  well  developed.  It  in- 
cludes the  Buff  and  Blue  limestones  of  the  first  state  survey,32  and  is  equiv- 
alent to  the  ''Trenton"  of  most  early  workers  and  to  the  still  earlier  St.  Peter 
Shell  Limestone.  Others  have  used  "Trenton"  to  include  both  Platteville 
and  Galena  formations.  Since  the  Galena  alone  is  approximately  equivalent 
to  the  type  Trenton  of  New  York,  the  name  Platteville  has  been  substituted. 

Lithologic  character.  In  this  area,  the  Platteville  consists  of  three  dis- 
tinct divisions;  the  basal  part,  or  Buff  limestone;  the  middle,  or  Blue  lime- 


31  Bain,  H.  F.,  Zinc  and  lead  deposits  of  northwestern  Illinois:  U.  S.  Geol.  Survey, 
Bull.    246,    p.    18,    1905. 

32  Shaw,   James,  Geol.   Survey  of  Illinois,   vol.  V,   pp.   104-13!*,   1873. 


54  DIXOX    QUADRANGLE 

stone,  and  the  upper  member,  for  which  the  name  Lowell  Park  is  here  pro- 
posed from  its  typical  development  in  Lowell  Park  and  along  the  road  north 
of  the  park.  The  Buff  limestone  is  a  buff  to  yellow-brown,  fine  to  coarse- 
grained, well-bedded,  magnesian  limestone,  which  carries  some  sand  grains 
in  a  carbonate  matrix  in  the  lower  beds,  and  contains  much  clay  but  no  inter- 
bedded  shale.  The  purer  beds  weather  to  a  light  brown,  rough,  porous, 
granular  rock,  which  in  hand  specimens  is  identical  with  some  of  the  dolo- 
mite in  the  Shakopee.  The  more  argillaceous  strata  break  down  to  thin, 
regular  laminae  and  produce  a  light  brown  clay,  which  often  feels  and  ap- 
pears sandy  because  of  included  dolomite  grains.  White  chert  is  common 
in  this  part  of  the  Platte\Tille. 

The  Blue  limestone  consists  of  a  lower,  highly  fossiliferous,  thick- 
bedded,  blue  limestone,  and  an  upper,  sparingly  fossiliferous,  crypto-crystal- 
line,  very  heavy-bedded,  blue  limestone  or  "glass  rock,"  which  contains 
brown  dolomitic  nodules  and  branching  masses.  The  lower  Blue  limestone 
is  deep  blue,  fine-grained,  somewhat  argillaceous,  free  from  sand  and  chert, 
and,  when  fresh,  has  strata  8  to  10  inches  thick.  Unlike  the  Platteville  to 
the  north  and  west,  no  interbedded  shale  occurs.  As  a  result  of  weather- 
ing, residual  clay  appears  between  the  irregular  limestone  laminations.  Pro- 
longed weathering  produces  a  gray,  or  in  some  beds,  a  buff  color,  and  breaks 
up  the  beds  into  lumpy,  lenticular  masses  ranging  up  to  two  inches  in  thick- 
ness and  six  inches  in  length.  The  surface  of  the  weathered  rock  is  covered 
with  a  characteristic  chalk- white  coating  of  calcium  carbonate,  so  that  the 
outcrop  looks  as  though  it  had  been  whitewashed. 

The  glass  rock  is  a  crypto-crystalline,  very  pure,  blue  to  buff,  brittle 
limestone  containing  numerous  nodules  and  irregular  masses  of  coarsely 
crystalline  dolomite.  The  texture,  conchoidal  fracture,  and  brittleness  give 
the  rock  its  name.  It  spalls  off  like  glass  under  impact,  but  is  a  dense,  hard 
stone  which  would  be  valuable  for  building  purposes  if  it  were  free  from  the 
magnesian  masses,  which  resemble  worm  borings  in  timber.  Because  the 
dolomite  is  porous  and  crystalline,  and  is  readily  attacked  by  ground  water, 
the  comparison  to  worm  work  may  be  carried  further,  for  the  disintegrated 
dolomite  sand  corresponds  to  the  half-eaten  "saw  dust"  left  by  the  worms 
in  timber.  On  the  whole,  the  glass  rock  is  less  easily  weathered  than  any 
other  rock  which  outcrops  in  the  area. 

The  Lowell  Park  consists  of  interbedded  gray  and  buff,  argillaceous, 
but  heavy-bedded  limestones,  and  coarse-grained,  deep  yellow-brown,  porous 
dolomites.  The  dolomite  is  in  every  way  typical  of  the  next  succeeding 
formation,  the  Galena,  and  in  small  outcrops  cannot  be  distinguished  litho- 
logically  from  it.  The  chalky,  earthy  limestones  are  more  like  the  impure 
portions  of  the  Buff  member.  The  chalky  beds  carry  abundant  fucoids,  and 
bedding  planes  are  marked  by  numerous  dendrites.     Weathering  reduces  the 


PLATTEVILLE   LIMESTONE  55 

dolomitic  beds  to  a  dark  yellow-brown  sand  of  dolomite  grains.  The  chalky 
beds  split  up  into  a  thin-bedded,  shaly  mass,  which  is  easily  eroded,  and 
accordingly  rarely  outcrops. 

Topographic  expression.  The  members  of  the  Platteville  all  resist 
weathering  processes  very  well,  the  Blue  being  the  most  resistant  and  the 
Lowell  Park  least.  The  formation  produces  narrow,  steep-sided  valleys; 
where  a  stream  cuts  through  the  limestone  into  the  soft  shale  and  sandstone 
below,  a  vertical  bluff  is  commonly  formed,  which  persists  as  the  dominant 
feature  of  the  topography  even  after  the  valley  is  widened  by  lateral  plana- 
tion.  Since  the  Platteville  protects  the  underlying  sandstone  from  rapid 
erosion,  vertical  cliffs  are  formed,  which  are  the  distinctive  and  alluring 
features  of  the  landscape  along  Rock  River  and  its  tributaries.  Solution 
and  frost  action  open  vertical  joints  and  horizontal  bedding  planes   (fig.  7), 


Fig.  7.     Outcrop  of  Platteville  limestone  in  NW.  *4  sec.  20,  T.  22  N.,  R.  11  E., 
showing  character  of  bedding,  jointing,  and  overlying  till. 

producing  a  good  imitation  of  masonry  walls  with  towers,  pinnacles  and  bat- 
tlements. This  characteristic  appearance  was  called  "castellated  topography" 
by  Owen,  the  first  geologist  to  study  this  formation  in  the  Mississippi  valley. 
He  grouped  the  Platteville  and  overlying  Galena  together  as  the  "Cliff  lime- 
stone," and  at  first  correlated  them  with  a  younger  formation  of  similar 
aspect  in  Ohio. 

Thickness  and  details  of  section.     The  thickness  of  the  Platteville  lime- 
stone ranges  from  100  to  125  feet,  distributed  as  follows : 

Lowell  Park  member 20-30  feet 

Blue  limestone 

Glass  rock    25-30  feet 

Fossiliferous    40-45  feet 

Buff   limestone    0-20  feet 


56  DIXON    QUADRANGLE 

The  Buff  member  varies  from  a  foot  or  two  to  a  maximum  thickness 
of  20  feet,  except  on  top  of  the  La  Salle  anticline,  where  it  is  usually  about 
6  feet  thick.     The  following  section  is  typical. 

Section   of   the   Buff   limestone   member,    Platteville    limestone,    in   ravine   in   the 
NE.  1,4  SW.  %  sec.  22,  T.  22  N.,  R.  9  E. 

Description  of  strata  Thickness 

Ft.        In. 
Blue  limestone 

Typical  "white-washed"  nodular  beds 

Covered 3  6 

Buff  limestone 

Very  ferruginous,  strongly  dolomitic,  yellow-brown  limestone,   ap- 
pearing sandy  on  surface  because  of  coarse  dolomite  grains ....       1  3 

Similar  to  above,  with  %-inch  sand  laminations  intercalated 4 

Light  brown,   dolomitic  limestone,  poorly  exposed 3  8 

Light  buff  to  deep  brown,  somewhat  sandy  dolomite 1 

Well-bedded,  rounded-grain  quartz  sandstone  with  dolomite  cement     . .  2 

Buff,    dense    limestone,    slightly    dolomitic,    much    sand    scattered 

through  limestone;   clay  in  wavy  bedding 2  2 

Very  fossiliferous,  buff  to  light  brown,  slightly  dolomitic  limestone     . .  10 

Buff    dolomitic   limestone   with    scattered    sand    grains   which   are 

abundant  in   lower  part 5  2 

Glenwood   shale    

Total,    Buff    limestone 14  7 

The  thickness  of  this  section  probably  should  be  increased  by  adding  the 
covered  strata,  making  a  total  of  18  feet. 

The  Blue  limestone  consists  of  40  to  45  feet  of  the  very  fossiliferous 
limestone  and  25  to  30  feet  of  glass  rock.  The  following  section  is  typical 
of  the  fossiliferous  zone. 

Section  of  lower,  fossiliferous  zone  of  Blue  limestone  member,   Platteville   lime-' 
stone.     Abandoned  quarry  in  the  SW.  %  NW.  %  sec.  22,  T.  22  N.,  R.  9  E. 

Description  of  strata  Thickness 

Ft.        In. 

Top  of  cliff,  covered 

Buff,  very  fine-grained  limestone,  weathers  white  on  surface,  develops 

lenses  or  lumps  on  weathering,  coarser-grained  than  beds  below....     11 
Thin-bedded,   argillaceous,  very   fine-grained,  blue   limestone,   weathers 
to   nodular   white-coated   surface.     Much   clay   along   surfaces   between 
lenses  or  nodules,  which  are  %  to  2  inches  thick.     This  bed  forms 
the  most  distinctive  castellated  bluffs  along  Rock  River  from  Dixon 

to    Devils    Backbone 10 

Blue,  fine-grained  limestone,  weathering  buff,  but  not  brown,  beds  2  to 

6  inches,  no  dolomite 6  2 


PLATTEVLLLE   LIMESTONE  57 

Section  of  lower,  fossiliferous   zone   of  Blue  limestone   member,  Platteville  lime- 
stone.   Abandoned  quarry  in  the  SW.  %  NW.  %  sec.  22,  T.  22  N.,  R.  9  E. — Concluded 

Description  of  strata  Thickness 

Ft.  In. 
Blue,  glass-rock  type,  sparingly  fossiliferous  limestone,  weathering  into 

angular,  thick  blocks  instead  of  usual  nodules 6  4 

Extremely    fossiliferous,    fine-grained,    blue    limestone,    weathering    to 

usual    "white-washed"    beds 2  6 

Irregular-bedded   blue    limestone,  with    50   per    cent    of   buff   dolomitic 

irregular  masses;  weathers  to  a  rough,  honey-combed  face 5  8 

Buff  limestone    

Total   fossiliferous   Blue   limestone 41  8 


The  glass  rock  is  not  readily  divisible  into  zones.  In  the  cement  plant 
quarry,  28  feet  of  typical  glass  rock  is  exposed.  The  original  thickness  has 
been  reduced  by  glacial  erosion.  The  following  section  indicates  the  com- 
mon relations  and  characteristics  of  the  glass  rock. 

Section  of  glass  rock  and  Lowell  Park  members  of  Platteville  limestone.     Aban- 
doned quarry,  in  the  NE.  %  NE.  y±  sec.  20,  T.  22  N.,  R.  9  E. 

Description  of  strata  Thickness 

Lowell  Park  member  Ft.        In. 

7  Chalky,  argillaceous,  soft,  buff  limestone 1  6 

6  Alternating  fine  and  coarse-grained,  buff  to  yellow-brown,  porous 

dolomite   and   dolomitic   limestone    containing    many    fucoids 

and   numerous   fossils    10  5 

Slight  erosional  unconformity 
Blue  limestone  member 
Glass  rock  zone 
5  Buff   to    light   brown,    tough,    massive,    fine-grained,    slightly 

magnesian  limestone,  with  numerous  dolomite  nodules  or 
masses;    weathers  into   six  to   ten-inch  thick,  well-jointed 

beds    6  9 

4  Typical,  deep  blue,  crypto-crystalline,  conchoidal  fracturing, 

dense,  brittle  limestone,  called  "glass  rock";  contains  dolo- 
mitic nodules,  increasing  in  amount  upward;   weathers  to 

solid,   angular,   gray   blocks 8  6 

3  Heavy-bedded,  dense,  blue  glass  rock,  with  a  few  irregular 

zones    which    weather    to    "whitewashed"    material;    most 
of  this  zone   turns   gray  and   breaks   into   angular   blocks 

on   weathering;    rare   fossils 12  6 

2           Fossiliferous  zone,  lower  Blue  limestone,  typical,  to  river  level     32 
1  Buff  limestone,  estimated  from  outcrops  upstream 15 

Total  Glass  rock   (3,  4  and  5) 27  9 

Total    Platteville    (1-7) 86  8 


58  DIXON    QUADRANGLE 

The  following  is  the  best  section  of  the  Lowell  Park  member  of  the 
Platteville,  and  contains  only  14  feet  more  than  the  section  immediately 
preceding. 

Section  of  Lowell  Park  member,  Platteville  limestone.    Roadside  exposures,  east 
side  NE.   %   SE.  %   sec.  18,   T.  22  N.,  R.  9  E. 

Description  of  strata  Thickness 

Feet 
Galena  dolomite 
Platteville   limestone 

Lowell  Park  member 

Buff    to    yellow-brown,    fine-grained,    argillaceous,    chalky,    soft 

limestone  in  well-defined  beds  4  to  8  inches  thick,  about....         12 
Yellow-brown     to     brown,     coarse-grained,     porous,     dolomitic, 
fucoidal,    wormy    limestone,    lithologically    very    similar    to 

Galena    limestone    14 

Blue  member 

Total,   Lowell  Park  member 26 

Areal  distribution.  The  Platteville  limestone  crowns  all  the  higher  hills 
between  Rock  River  and  Pine  Creek  and  occurs  in  the  valley  sides  farther 
west.  From  Pine  Creek  southward,  it  occupies  a  narrowing  zone  along  the 
right  bank  of  the  main  stream  and  extending  under  the  valley  train  to  the 
western  edge  of  the  quadrangle.  It  covers  most  of  the  upland  south  of 
Rock  River,  west  of  Chamberlain  Creek  and  north  of  the  Chicago  and 
Northwestern  Railway.  Because  of  a  heavy  cover  of  glacial  till,  it  is  not 
well  known  south  of  the  railroad,  but  it  covers  a  wide  belt  extending  south- 
eastward from  Dixon  to  Lee  Center.  It  also  underlies  most  of  the  upland 
northeast,  east  and  southeast  of  Franklin  Grove.  Details  of  its  distribution 
are  shown  in  Plates  I  and  V. 

Paleontologic  character.  The  following  list  indicates  the  fossils  which 
were  collected  from  the  Platteville  limestone  in  this  area.  As  in  the  case 
of  the  other  fossil  lists,  the  determinations  have  been  checked  by  Dr.  J.  J. 
Galloway.  The  small  number  of  forms  obtained  from  the  Lower  Buff 
and  the  Lowell  Park  is  not  evidence  of  the  small  amount  of  life  existing 
during  the  early  and  late  Platteville  time,  but  results  from  the  partial  dolo- 
mitization  which  has  affected  much  of  each  member.  There  is  no  reason 
to  postulate  a  faunal  difference  between  the  different  members,  but  their 
contents  are  indicated  in  separate  columns  for  the  sake  of  an  accurate  record. 


PLATTEVUXE   LIMESTONE 


59 


Table  2. — Fossils  collected  from  the  Platteville   limestone,  Dixon  quadrangle 


Fossils 


Lower 
Buff 


Blue 


Lowell 
Park 


Arthropora   simplex  Ulrich 

Batostoma  cf.  magnopera  Ulrich 

Batostoma   winchelli   Ulrich 

Carabocrinus  cf.  radiatus  Billings 

Clathrospira   subconica   Hall 

Columnaria    halli    Nicholson 

Constellaria  varia  Ulrich 

Crania   trentonensis    Hall 

Cyrtoceras  sp. 

Cyrtodonta  obliqua  Meek  and  Worthen 

Dalmanella  testudinaria  Dalman 

Dekayella   praenuntia   Ulrich 

Dinorthis   pectinella   Emmons 

Encrinurus    vannulus    Clarke 

Endoceras  proteiforme  Hall 

Eridotrypa  aedilis   Eichwald 

Eridotrypa  aedilis  minor  Ulrich 

Escharopora  subrecta  Ulrich 

Eurychilina  reticulata  Ulrich 

Gonioceras    occidentale    Hall 

Hemiphragma    irrasum    Ulrich 

Homotrypa  minnesotensis  Ulrich 

Illaenus   punctatus   Raymond 

Leperditia    f abulites   Conrad 

Leptaena  charlottae  Winchell  and  Schuchert. 

Lichenaria  typa  Winchell  and  Schuchert 

Lingula  elderi  Whitfield 

Liospira  obtusa  Ulrich  and  Scofield 

Liospira  progne   Billings , 

Liospira  vitruvia  Billings 

Lophospira   bicincta   Hall 

Lophospira  obliqua  Ulrich 

Ophiletina  sublaxa  Ulrich  and  Scofield 

Orthis   tricenaria   Conrad 

Orthoceras  sp 

Orthoceras  cf.  sociale  Hall 

Pachydictya  acuta  Hall 

Phragmolithes   fimbriatus  Ulrich  and   Scofield 

Pianodema    subaequata    Conrad 

Plectambonites    sericeus    Sowerby 

Rafinesquina  alternata  Emmons 

Rafinesquina  minnesotensis  N.  H.  Winchell... 

Rhinidictya  exigua  Ulrich 

Rhinidictya   grandis   Ulrich 

Rhinidictya  mutabilis  Ulrich 


60 


DIXON    QUADRANGLE 


Table   2. — Fossils   collected   from   the   Platteville    limestone,    Dixon    quadrangle- 
Concluded 


Fossils 


Lower 
Buff 


Blue 


Lowell 
Park 


Rhinidictya  trentonensis  Ulrich 

Salpingostomy  buelli   Whitfield 

Scenidium   anthonense    Sardeson 

Scolithus  sp 

Spyroceras  bilineatum  Hall   

Streptelasma  corniculum  Hall 

Streptelasma  profundum  Conrad  (Owen)    

Strophomena  emaciata  Winchell  and  Schuchert.  . . . 

Strophomena  incurvata   Shepard 

Strophomena  scofieldi  Winchell  and   Schuchert 

Strophomena  trentonensis  Winchell  and   Schuchert. 

Strophomena  winchelli  Hall  and  Clarke 

Subulites  regularis  Ulrich  and  Scofield 

Thaleops  ovatus   Conrad 

Trochonema  beachi  Whitfield 

Trochonema   umbilicatum   Hall 

Zygospira  nicoletti  Winchell  and  Schuchert 

Zygospira  recurvirostris  Hall 


Correlation.  The  Platteville  limestone  was  deposited  in  Middle  Ordo- 
vician  time.  The  Buff  and  Blue  members  are  correlated  with  the  Upper 
Stones  River  series  of  Tennessee  and  the  Chazy-Lowville  of  New  York. 
The  Lowell  Park  member  is  the  same  in  age  as  the  Decorah  shale  of  Iowa. 
A  local  term  has  been  used  here  in  place  of  Decorah,  since  a  limestone,  in- 
stead of  shale,  is  present  in  this  quadrangle,  and  also  because  the  original 
definition  of  Bain33  and  later  of  Calvin34  who  defined  the  Decorah  shale, 
was  that  the  Platteville  included  all  limestone  between  the  St.  Peter  and 
Galena  formations.  The  Black  River  formation  of  New  York  is  correlated 
with  the  Decorah  and  with  the  Lowell  Park  member  of  the  Platteville. 

Relations  to  adjacent  formations.  As  already  stated,  there  is  no  evi- 
dence in  this  quadrangle  of  erosion  following  St.  Peter  deposition,  but  the 
Glenwood  shale  and  the  Buff  member  of  the  Platteville  are  thin  or  entirely 
absent  on  top  of  the  La  Salle  anticline.  The  Buff  does  not  consistently  ex- 
tend farther  up  the  flanks  than  the  Glenwood ;  both  may  be  present  and  both 
thin.  It  seems  that  conditions  on  the  anticline  were  unfavorable  for  deposi- 
tion until  the  Blue  limestone  was  formed.     Cady35  found  evidence  of  slight 


33  Bain,   H.    F.,    U.    S.    Geol.    Survey   Bull.    246,    p.   IS,    1905. 

3i  Calvin,  S.,  Geology  of  Winneshiek  County:  Iowa  Geol.  Survey,  vol.  XVI,  p.  81, 
1906. 

35Cady,  G.  H.,  Geology  of  the  Hennepin  and  La  Salle  quadrangles:  Illinois  State 
Geol.    Survey   Bull.    37,   p.    39,    1919. 


GALENA    DOLOMITE  61 

erosion  at  this  horizon  30  miles  farther  south  along  the  anticline.  The 
boundary  between  the  Buff  and  Blue  members  is  gradational  without  a  sharp 
change  in  material  or  evidence  of  disconformity.  Between  the  Blue  and 
Lowell  Park  members,  an  erosional  unconformity  of  slight  relief  is  found 
at  many  places.  This  is  well  exhibited  in  the  quarry  beside  Ravine  Road, 
300  feet  south  of  Rock  River,  in  Dixon.  (SE.  %  SW.  }i  sec.  33,  T.  22  N., 
R.  9  E.)  Depressions  of  six  to  eight  inches  developed  in  the  top  of  the 
Blue  before  the  Lowell  Park  was  deposited.  No  residual  soil  or  chert 
marks  this  unconformity  within  the  quadrangle,  and  there  is  no  evidence  of 
important  erosion.  The  Galena  formation  succeeds  the  Lowell  Park  with- 
out sharp  change  in  sediments  or  apparent  erosion.  Argillaceous  matter 
decreases  and  magnesia  increases  at  the  contact,  but  sedimentation  was  prob- 
ably continuous. 

GALENA   DOLOMITE 

Name.  The  Galena  dolomite  was  so  named  by  James  Hall36  because 
it  was  the  principal  source  of  lead  in  Mississippi  Valley,  galena  being 
the  name  of  the  common  lead-ore  mineral. 

Lithologic  character.  Except  the  St.  Peter,  the  Galena  is  the  most  uni- 
form of  the  formations  in  the  area.  It  is  a  thick-bedded,  porous,  cherty, 
coarsely  crystalline,  buff  to  yellow-brown  dolomite.  In  fresh  exposures, 
the  strata  average  30  inches  in  thickness  ;  weathered  outcrops  show  beds 
6  to  10  inches  thick.  Originally  a  limestone,  the  formation  has  been  thor- 
oughly dolomitized  with  accompanying  decrease  in  volume.  This  decrease 
in  volume  was  accomplished  without  perceptible  slumping  or  subsidence, 
by  increase  of  pore  space,  so  that  the  rock  is  very  porous,  yields  water  read- 
ily to  wells,  and  is  generally  deeply  weathered  in  outcrops.  White  and 
buff-colored  cherts  are  found  throughout  the  formation.  They  are  not 
common  in  the  basal  30  feet,  but  are  abundant  above  that  level.  Bryozoa 
are  rather  numerous  in  the  white  chert. 

The  entire  formation  consists  of  crystalline  dolomite,  the  crystals  rang- 
ing from  microscopic  size  to  2  mm.  in  diameter.  Weathering  removes  the 
cement  between  the  crystals  or  disintegrates  the  rock,  so  that  a  sandy  residue 
of  dolomitic  grains  results.  Where  very  fresh,  the  rock  is  gray-buff,  but 
on  all  natural  exposures  it  is  buff  to  deep  yellow-brown.  There  is  not  suffi- 
cient iron  to  cement  the  residual  soil  or  to  segregate  into  masses  of  limonite, 
as  in  the  Shakopee,  but  the  disintegrated  rock  is  always  colored  a  deep 
brown.  Well-developed  vertical  joints  occur  throughout  the  rock.  Bluff 
faces  are  vertical,  the  rock  having  broken  free  along  a  joint  plane,  and  on 
such  faces,  the  rock  has  a  rough,  granular,  rugged  surface,  marked  by 
numerous  solution  cavities.     Where  there  is  much  vegetation,  the  rock  sur- 


36  Foster,    J.    W.,    and   Whitney,    J.    D.,    Geology    of    the    Lake    Superior    Land    Dis- 
trict:  32d  Cong.,   spec,   sess.,   Senate   Doc.    4,   p.    146,   1851. 


62 


DIXON    QUADRANGLE 


face  is -gray,  probably  because  organic  matter  reduces  and  helps  to  dissolve 
the  iron  oxide  from  the  surface.  In  the  absence  of  plant  life,  the  surface 
weathers  a  deeper  brown  than  the  interior  of  the  dolomite.  Figures  8  and 
9  illustrate  the  normal  aspect  of  the  Galena  dolomite. 

Topographic  expression.  This  formation  has  less  resistance  to  solu- 
tion and  freezing  water  than  any  of  the  other  carbonate  rocks  of  the  area. 
Accordingly  its  valley  sides  are  readily  reduced  to  gentle  slopes,  bluffs  occur- 
ring only  where  downward  erosion  is  unusually  rapid,  as  along  Rock  River  in 
the  city  of  Dixon.  In  the  uplands,  the  Galena  outcrops  have  been  reduced 
until  they  merge  imperceptibly  into  the  prairie.  Quarries  have  been  opened 
in  sees.  28  and  30,  South  Dixon  Township  (T.  21  N.,  R.  9  E.)  and  in  sec. 
20,  Ashton  Township  (T.  22  N.,  R.  11  E.),  where  the  rock  was  discovered 
in  plowing. 


Fig.  8.    Galena  dolomite  in  a  quarry  in  NE.  ^4  sec.  8,  T.  21  N.,  R.  9  E„ 
showing  typical  massive  beds  which  weather  to  thinner  strata. 

Thickness.  At  no  place  is  more  than  60  feet  of  this  formation  ex- 
posed. It  is  so  uniform  that  individual  beds  cannot  be  correlated  from  one 
section  to  another.  For  this  reason,  a  general  section  with  closely  estimated 
thickness  cannot  be  built  up  from  the  limited  exposures.  The  Platteville- 
Galena  contact  at  the  Rock  River  dam  in  Dixon  is  680  feet  above  sea  level. 
This  surface  cannot  be  traced  southwestward  underground  because  well 
logs  do  not  distinguish  between  the  Galena  and  Plattcville.  It  will  be  found 
at  about  630  feet  under  the  center  of  section  8,  provided  the  dip  continues 
the  same  as  in  the  area  northeast  of  Dixon.  On  this  assumption  of  uniform 
dip,  the  Galena  may  be  said  to  have  a  thickness  of  about  150  feet  in  this 
area.     Southward  the  surface  slopes  approximately  parallel  to  the  dip  and 


GALENA    DOLOMITE 


63 


may  be  nearly  the  original  top  of  the  Galena,  from  which  the  overlying 
Maquoketa  shales  have  recently  been  removed.  The  only  evidence,  how- 
ever, for  this  hypothesis  is  the  parallelism  between  bedding  planes  and  sur- 
face topography. 

The  only  identifiable  horizons  in  the  Galena  are  a  zone  of  Receptaculites 
oweni  about  six  feet  above  the  Lowell  Park  member  of  the  Platteville;  a 
marked  increase  in  chert  about  30  feet  above  the  base,  and  another  Recep- 
taculites zone  about  45  feet  higher,  or  75  feet  above  the  base.     Hand  speci- 


-v;€>'-*;.:V^:\  *■ 


Fig.  9.    Close  view  of  exposure  in  figure  8,  show- 
ing cellular  structure  produced  by  solution. 

mens  from  various  horizons  cannot  be  differentiated.  The  oil  rock  and 
interbedded  shales  which  are  conspicuous  in  northwestern  Illinois  are  en- 
tirely absent  in  this  area.  It  is  probable  that  this  absence  of  impervious 
beds  favored  the  dolomitization  of  the  formation,  which  is  here  much  more 
complete  than  at  places  north  and  west.37 


87  Calvin,   Samuel,   and  Bain,   H.  F.,   Geology  of  Dubuque  County 
vey,  vol.  10,  pp.   402-411,   1900. 


Iowa  Geol.    Sur- 


64  DIXON    QUADRANGLE 

Areal  distribution.  The  Galena  is  the  highest  indurated  rock  in  this 
area  and  has  been  removed  from  the  higher  parts  of  the  regional  structure. 
Although  the  area  underlain  by  Galena  is  less  than  that  covered  by  any 
other  formation  except  possibly  the  "New  Richmond"  sandstone,  its  out- 
crop is  larger  than  that  of  any  formation  except  the  St.  Peter  and  the  Platte- 
ville.  As  shown  on  Plate  V,  the  Galena  covers  most  of  the  western  part 
of  the  quadrangle.  North  of  Rock  River,  its  outcrop  is  dissected  by  numer- 
ous tributaries,  and  the  dolomite  is  confined  chiefly  to  the  uplands.  South 
of  the  Rock  River  and  Chicago  Road  from  Dixon  to  Lee  Center,  the  Galena 
covers  practically  all  the  surface.  The  line  between  the  Platteville  and 
Galena,  which  extends  southeastward  from  Dixon,  is  the  least  accurately 
mapped  of  all  the  boundaries  on  the  map,  for  here  the  drift  cover  is  heaviest 
and  well  records  do  not  distinguish  between  the  two  formations. 

Pahontologic  character.  Because  of  the  thorough  dolomitization  of 
the  rock,  the  original  fossil  content  is  largely  destroyed.  Such  forms  as 
remain  are  usually  preserved  only  as  molds  of  coarse-grained  dolomite  and 
most  of  them  cannot  be  identified.  The  following  is  a  list  of  species  found 
during  this  study.  As  in  the  case  of  the  Platteville  fauna,  Dr.  J.  J.  Gallo- 
way has  checked  and  criticized  the  determinations. 

Fossils  collected  from  the  Galena  dolomite  in  the  Dixon  quadrangle 

Amplexopora  sp. 

Bellerophon  troosti  D'Orbigny 

Bucania  nashvillensis  Ulrich 

Fusispira  angusta  Ulrich  and  Scofield 

Hebertella  sp. 

Holopea  excelsa  Ulrich  and  Scofield 

Homotrypa  similis  Foord 

Homotrypa  sp. 

Hormotoma  gracilis  Hall 

Hormotoma  major  Hall 

Illaenus  americanus  Billings 

Ischadites  iowensis  Owen 

Liospira  americanus  Billings 

Lophospira  augustina  Billings 

Lophospira  bicincta  Hall 

Lophospira  obliqua  Ulrich 

Rafinesquina  alternata  Emmons 

Rafinesquina  minnesotensis  N.  H.  Winchell 

Receptaculites  oweni  Hall 

Rhinidictya  sp. 

Rhynchotrema  increbescens  Hall 

Sinuites  cancellatus  Hall 

Sinuites  cancellatus  trentonensis  Ulrich  and  Scofield 

Streptelasma  corniculum  Hall 

Strophomena  trilobata  Owen 

Trochonema  umbilicatum  Hall 

Vanuxemia  wortheni  Ulrich 


YOUNGER  PALEOZOIC   FORMATIONS  65 

Correlation.  The  Galena  is  regarded  as  the  Mississippi  Valley  equiv- 
alent of  the  Trenton  in  New  York.  "Trenton"  was  used  for  some  time  in 
this  region  as  the  name  for  the  Platteville,  and  reports  on  Mississippi  Valley 
geology  which  apply  Trenton  to  a  limestone  or  shale  group  are  describing 
Platteville  limestone  and  Decorah  shale,  or  some  part  of  them. 

Relations  to  adjacent  formations.  In  this  area,  there  is  no  evidence  of 
any  interruption  of  deposition  between  the  Lowell  Park  member  of  the 
Platteville  and  the  Galena.  The  dolomitic  portion  of  the  Lowell  Park  is 
similar  in  every  way  to  typical  Galena,  and  is  repeatedly  interbedded  with 
less  magnesian  limestones  which  resemble  the  Buff  member  of  the  Platte- 
ville. So  striking  is  this  relation  that  Shaw38  described  the  Lowell  Park 
member  as  "beds  of  transition."  Trowbridge  and  Shaw39  have  described 
and  figured  an  erosional  unconformity  at  the  base  of  the  Galena,  but  no  evi- 
dence of  such  a  relation  was  found  in  this  quadrangle.  Erosion  has  re- 
moved any  rocks  that  formerly  overlay  the  Galena  in  this  area,  and  there  is 
no  evidence  of  the  relation  of  the  Galena  to  any  higher  beds,  except  the 
glacial  deposits. 

YOUNGER  PALEOZOIC  FORMATIONS 

The  Galena  dolomite  is  the  youngest  indurated  formation  now  known 
in  this  quadrangle.  Above  the  Galena,  the  Maquoketa  shales  were  origi- 
nally deposited.  These  outcrop  in  all  directions  from  this  area,  except  due 
north,  and  presumably  were  once  present  here.  The  Maquoketa  is  known 
in  outcrops  or  wells  in  Polo,  Woosung,  and  Nelson  townships,  west  of  this 
quadrangle,  and  in  Harmon  and  Marion  townships  to  the  south.  There  may 
be  remnants  of  the  Maquoketa  within  the  Dixon  quadrangle  in  South  Dixon 
or  Marion  Township,  but  if  such  beds  occur  they  are  buried  beneath  the 
glacial  drift  and  no  available  logs  record  their  presence.  Certainly  no  im- 
portant amount  of  these  shales  remains. 

The  Niagaran  limestone  probably  once  covered  this  area  also,  for  its 
outcrops  surround  the  Dixon  quadrangle  just  as  the  Maquoketa  exposures 
do,  but  at  a  greater  distance.  Weathering  and  stream  erosion  removed 
most  or  all  of  it  before  glaciation.  Outliers  of  the  formation  may  have 
persisted  here  until  glaciation,  just  as  "mounds"  capped  by  Niagaran  lime- 
stone outliers  are  prominent  topographic  features  in  the  Driftless  Area  to- 
day. If  there  were  such  remnants,  they  were  destroyed  during  the  glacial 
invasions,  and  the  Niagaran  and  Maquoketa  rocks  were  ground  up  and 
mingled  with  other  glacial  debris  in  the  till.  Pebbles  and  angular  frag- 
ments of  these  formations  have  been  identified  here,  but  may  have  been 
carried  in  from  the  northeast  by  the  ice. 


38  Shaw,  James,  Geology  of  Lee  County:  Geol.  Survey  of  Illinois,  vol.  5,  p.  130,  1873. 

39  Trowbridge,    A.    C.    and    Shaw,    E.    W.,    Galena    and    Elizabeth    quadrangles:    Illi- 
nois State  Geol.  Survey  Bull.  26,  pp.  54,  61,  1916. 


66  DIXOX    QUADRANGLE 

There  is  no  evidence  that  later  Paleozoic  or  Mesozoic  formations  ever 
covered  the  region. 

Cenozoic  Group 

pleistocene  system 

As  shown  on  Plate  I.  glacial  deposits  cover  most  of  the  npland  areas. 
Rock  and  Kyte  valleys  have  heen  deeply  tilled  by  valley  trains,  which  neces- 
sitated deposition  in  most  tributary  valleys  also. 

rRE-ILLIXOTAX    DEPOSITS 

Xo  pre-Illinoian  soils  are  now  exposed  beneath  the  till.  Where  the 
base  of  the  till  is  not  weathered,  the  surface  rock  normally  is  fresh,  and  in 
many  places  is  polished.  An  augur-boring  beside  the  Lincoln  Highway  a 
mile  and  a  half  east  of  Dixon  encountered  residual  soil  on  the  Galena  dolo- 
mite, under  six  feet  of  calcareous  till.  This  was  a  dark  red-brown,  com- 
pact, coherent  clay,  such  as  is  typical  of  residual  soils  from  limestone. 

Wells  in  Ashton  Township  (T.  22  N.,  R.  11  E.")  and  one  in  sec.  18, 
South  Dixon  Township  ^T.  21  X..  R.  9  E.)  have  penetrated  the  Illinoian  till 
and  encountered  a  forest-soil  bed  containing  decayed  tree  fragments  and 
yielding  a  dark-colored,  disagreeable-tasting  water.  In  each  case  the  well 
was  abandoned,  and  no  evidence  was  obtained  of  an  underlying  till,  if  one 
exists.  The  character  of  the  material  does  not.  as  popularly  supposed,  in- 
dicate pre-Illinoian  swamps  at  these  places,  for  any  buried  plant  matter 
may  assume  this  apparent  swamp-debris  character  after  long  standing  in  a 
saturated  condition  in  or  under  the  till. 

No  clear  proof  is  known  of  X^ebraskan  or  Kansan  glacial  deposits  in 
this  area.  A  few  thoroughly  weathered  glacial  boulders  occur  in  unleached 
and  unoxidized  light  yellow  or  blue  Illinoian  till.  So  complete  is  the 
weathering  of  some  of  the  boulders  that  they  crumble  readily  between  the 
lingers,  although  they  had  originally  been  gabbro,  diabase,  greenstone,  and 
granite.  The  sides  of  the  boulders  are  faceted,  striated  and  ground  smooth 
by  the  ice.  Subsequent  exposure  developed  concentric  weathering  bands 
in  the  basic  rocks,  paralleling  the  glaciated  faces.  These  boulders  accord- 
inglv  represent  an  earlier  period  of  glaciation,  in  which  the  fresh  rock  was 
abraded  to  its  present  form  :  they  were  weathered  during  one  or  more  in- 
terglacial  epochs,  and  while  frozen  solid,  were  picked  up  by  the  Illinoian 
ice  and  incorporated  in  the  till  of  that  epoch.  Although  the  boulders  indi- 
cate a  pre-Illinoian  glaciation.  there  is  no  satisfactory  evidence  that  they 
were  in  this  area  before  Illinoian  time.  If  they  could  be  gathered  by  the 
ice,  they  could  be  transported  an  indefinite  distance,  but  the  large  number  of 
these  boulders  suggests  that  they  have  not  travelled  far  and  accordingly 
suggests  pre-Illinoian  glaciation  of  this  region. 


ILLINOIAN   AND   IOWAN    (?)    TILLS  67 

ILLINOIAN    AND    IOWAN     (?)     TILLS 

Introduction.  Covering  most  of  the  uplands  is  a  typical  glacial  till,  con- 
sisting chiefly  of  material  from  the  local  limestone  and  sandstone  formations 
and  the  soil  which  formerly  covered  the  area.  Mixed  with  it  is  a  consider- 
able amount  of  material  which  may  belong  to  formations  entirely  destroyed 
by  the  glacier,  such  as  fragments  of  the  Niagaran  limestone.  As  outlined 
above,  this  formation  possibly  outcropped  in  this  area  in  rounded  hills,  as 
it  does  today  in  northwestern  Illinois,  and  southwestern  Wisconsin,  although 
it  may  have  been  entirely  removed  before  the  coming  of  the  glacier.  If 
the  latter  is  the  case,  the  Niagaran  fragments  found  in  the  area  came  from 
the  east.  Less  important  than  either  of  these  sources,  but  much  more 
prominent  because  of  their  unusual  color  and  texture,  are  the  igneous  and 
metamorphic  rocks  from  Canada.  Such  rocks  attracted  the  attention  of 
the  first  travelers  across  the  prairies  because  they  were  so  different  from 
any  visible  masses  of  bed  rock.  In  fact,  the  Indians  first  noticed  the  pres- 
ence of  unusual  boulders,  and  one  striking  example  in  Minnesota  was  singled 
out  by  them  for  special  reverence,  including  offerings  and  ceremonial  paint- 
ings with  vermilion.  The  rock  gave  its  name  to  the  present  village  of  Red 
Rock,  Minnesota,  although  under  its  paint  it  is  a  gray  granite.40 

In  a  series  of  careful  counts  of  boulders  and  pebbles  in  the  till,  the 
average  showed  12  per  cent  of  crystalline  rocks.  If  it  were  possible  to  study 
all  sizes  of  material,  this  proportion  would  be  greatly  reduced,  for  the  soft 
sediments  of  the  Paleozoic  contributed  a  much  larger  proportion  of  the  sand 
and  rock  flour  than  they  did  of  the  pebbles  and  larger  material.  Conversely, 
of  the  large  boulders,  a  much  larger  percentage  is  crystalline,  for  the  sedi- 
ments break  rather  easily  along  their  stratification  planes  and  do  not  form 
large  masses.  A  list  of  the  different  types  of  crystallines  found  includes 
practically  every  common  type  of  rock.  There  are  granites,  syenites,  dio- 
rites,  gabbros  and  peridotites  of  the  coarse-grained  igneous  rocks ;  rhyolites, 
andesites  and  basalts  of  the  lavas ;  and  gneisses,  schists,  quartzites  and  slates 
of  the  metamorphic  series.  The  red  rock  in  Dixon  Park  is  red  felsite 
porphyrite,  very  similar  to  much  of  the  lava  in  the  Michigan  copper  dis- 
trict ;  and  the  gray  gneiss  in  Oregon,  marking  the  site  of  the  Lincoln-Douglas 
debate,  is  typical  of  the  Grenville  series  of  Ontario.  A  petrologist  ac- 
quainted with  the  Ontario  crystallines  could  find  specimens  of  most  of  them 
in  the  unique  collection  assembled  about  the  Reed  home  in  Watertown.  An 
unusual  constituent  of  the  till  is  coal,  which  is  found  in  quarter-inch  pebbles 
at  several  places  in  the  area,  notably  in  a  ravine  in  sec.  16,  South  Dixon 
Township  (T.  21  N.,  R.  9  E.). 


^"Keating,  W.  H.,  Narrative  of  an  expedition  to  the  source  of  St.  Peter's  River, 
performed  in  1823,  vol.  1,  pp.  200,  263,  281-288.  Quoted  by  Martin,  Lawrence,  riiysi- 
ography  of  Wisconsin:   Wisconsin   Geol.   and  Nat.   Hist.   Survey   Bull.    36,   p.    73,    1916. 


6S  DIXOX    QUADRANGLE 

The  till  when  deposited  was  a  blue-gray,  sticky  clay,  such  as  is  seen 
today  in  the  beds  of  Fivemile  Branch  where  it  crosses  the  south  line  of  sec. 
27,  South  Dixon  Township  and  Threemile  Branch  in  sees.  19,  21  or  14. 
Blue  till  is  commonly  found  in  well  drillings,  and  less  often,  in  cellar  exca- 
vations. 

On  exposure,  the  till  is  oxidized  to  a  light  yellow-brown,  and  the  car- 
bonates are  dissolved  from  the  limestone  pebbles  and  powder.  Fresh  till 
is  popularly  called  boulder  clay  because  weathering  has  not  removed  any 
of  its  original  constituents.  Weathered  till  is  less  coherent;  the  limestone 
boulders  have  been  dissolved,  and  many  of  the  crystalline  pebbles  have  dis- 
integrated more  or  less.  The  Illinoian  till  commonly  develops  a  rough 
cleavage  or  fracture  on  weathering  which  divides  the  till  into  well-denned 
blocks. 

The  Illinoian  till  was  spread  out  in  a  remarkably  smooth  plain,  cover- 
ing all  of  this  area.  It  had  little  of  the  "knob  and  kettle"  topographv  often 
shown  by  fresh  till.  Those  areas  which  have  surtered  least  erosion  since 
glaciation  are  today  the  areas  of  least  relief.  Only  two.  small  undrained 
depressions  are  known  in  this  original  surface.  They  are  in  sees.  10  and 
11.  South  Dixon  Township,  and  are  so  shallow  that  they  are  not  represented 
on  the  topographic  map.  The  Iowan  (  ?)  till  forms  a  low.  rolling  ridge 
across  the  southern  end  of  the  quadrangle.  The  northern  side  of  this  ridge 
was  taken  as  the  approximate  limit  of  Iowan  ( ?)  till,  since  the  relations  of 
the  two  tills  are  masked  everywhere  by  a  heavy  cover  of  loess. 

As  a  result  of  its  mode  of  deposition,  the  thickness  of  the  till  originally 
varied  from  the  thinnest  possible  deposit  to  more  than  1S5  feet.  A  well  in 
the  XE.  :_  sec.  "29.  South  Dixon  Township,  penetrated  1ST  feet  of  till  with- 
out reaching  bed  rock,  but  within  both  a  mile  to  the  east,  and  a  mile  and  a 
quarter  to  the  west,  rock  outcrops  through  the  till.  Depth  of  till  shown 
in  deep  wells  in  the  southern  part  of  the  area  is  indicated  by  tables  3  and  1. 

Average  depth  of  glacial  till  can  be  estimated  from  well  logs,  but  these 
give  only  a  minimum  estimate  of  the  total  depth  of  hlling.  Averages  of 
depths  to  rock  in  the  wells  over  a  given  area  give  an  idea  of  the  total  amount 
of  tilling,  but  again  the  ligure  is  too  low.  because  any  well  that  stops  short 
of  rock  reduces  the  average  below  its  proper  value,  and  there  are  few  deep 
wells  in  the  area,  as  water  is  commonly  obtained  within  75  feet  of  the  sur- 
face. The  maximum  known  depth  of  Illinoian  till  tilling  is  1ST  feet.  South 
of  the  Chicago  and  Northwestern  Railway,  the  depths  of  39  wells  in  the 
Illinoian  till  area  are  known.  The  average  depth  to  rock,  or  to  the  bottom 
of  the  well  where  rock  was  not  reached,  is  65  feet.  Assuming  an  average 
thickness  for  the  loess  of  6  feet  ever  this  area  where  erosion  of  the  till  lias 
been  slight,  the  Illinoian  till  must  have  averaged  at  least  60  feet  in  thick- 
Ill  the  area  of  Iowan   (  ?)   drift,  seven  wells  encountered  rock  at  an 


ILLINOIAN    AND    IOWAN     (?)     TILLS 


69 


average  depth  of  75  feet,  and  twenty- four  wells  that  did  not  pass  through 
the  till  have  an  average  depth  of  78  feet.  If  the  loess  was  6  feet  thick  on 
the  average,  the  combined  Illinoian  and  Iowan  (  ?)  till  sheets  averaged  at 
least  70  feet  in  thickness. 

Originally  the  till  covered  practically  the  entire  area,  but  it  has  been 


Table  3. — Wells  not  reaching  rock  in  the  southwestern  part  of  Dixon  quadrangle 


Location  of  well 


Part  of  sec. 


NE.    %     

NE.    %     

SW.   corner    .... 

SW.    1,4    ... 

SE.   corner    

SW.    14    

Center  E.  line.. 
Center  N.  line.. 
W.  line  NW.  % 
W.  line  NW.  % 
SW.    cor.    SE.    y± 

sw.  14   

sw.  14   

Center  W.   line .  . 
NW.   corner    .  . .  . 
NW.   corner 
NE.    corner    .... 

NE.   14    

NW.    14    

NE.   14    

NW.    corner    .... 

SW.    14    

NW.    14    

NW.   corner    .... 

NW.    %    

N.  line   SE.    14 .  . 

SE.    14    

NW.    14    

NE.    1/4    

Center  W.  % . . . 
SW.  14    


sec. 


T.N. 


19 

29 

29 

32 

32 

33 

33 

34 

34 

34 

34 

35 

36 

3 

3 

3 

4 

5 

5 

3 

3 

4 

4 

4 

6 

31 

31 

32 

32 

33 

35 


21 
21 
21 
21 
21 
21 
21 
21 
21 
21 
21 
21 
21 
20 
20 
20 
20 
20 
20 
20 
20 
20 
20 
20 
20 
21 
21 
21 
21 
21 
21 


R.  E. 


9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

9 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 

10 


Total  depth 
Feet 


58 
187 

40 

40 

90  + 

90 

40 

70 

78 

80 

97 
130 

50 

43 

90 

45 

65 
103 
100  + 
103 

83 

72 

30 

96 

75 

66 

75 

40 

90 

75 
103 


removed  from  a  strip  roughly  three  miles  wide  along  Rock  River  and  from 
similar  areas  adjacent  to  the  larger  streams.  As  shown  on  Plate  I,  till  al- 
most entirely  covers  the  southern  third,  and  about  half  covers  the  eastern 
third  of  the  area.  In  the  central  and  northwestern  areas,  it  has  been  eithcr 
removed  entirely  or  greatly  reduced  in  thickness. 


70 


DIXON    QUADRANGLE 


Age  of  the  till.  The  till  of  the  quadrangle  belongs  to  at  least  two  dif- 
ferent epochs,  the  Illinoian  and  the  Iowan  (?).  There  is  only  slight  evi- 
dence of  a  pre-Illinoian  drift,  as  cited  on  page  66.  The  Illinoian  covers 
the  greater  part  of  the  area,  the  Iowan  (?)  being  confined  to  the  extreme 
southern  part.  The  separation  was  made  by  Leighton  after  a  broad  study 
of  northwestern  Illinois,  on  the  basis  of  (1)  the  degree  of  weathering  and 
erosion  of  the  till,  (2)  the  relations  to  the  loess,  and  (3)  the  existence  of  a 
low  marginal  ridge  in  this  quadrangle,  limiting  the  area  of  fresher  drift. 
These  lines  of  evidence  are  considered  in  order.41 

1.  Sixty-six  borings,  made  within  the  Iowan  (?)  area  of  this  quad- 
rangle and  to  the  east  and  south  to  the  outwash  along  Green  River,  showed 


Table  4. — Deep  wells  in  the  southwestern  part  of  Dixon  quadrangle  with  depth 

to   rock   only 


Location  of  well 


Part  of  sec. 


Center     

SE.  corner  .  . . 
SB.  corner  .  .  . 
NW.  !/4  SW.  % 
Center   E.   line. 


NE.  %  NW.  14.. 
NE.    14   NW.    % .  . 

SW.    %    

NE.  corner   

Center  W.  line.  . 
NW.  cor.  SW.  14 
E.  line  SE.  &  .  .  . 
S.   line    SW.    U.. 


sec. 

T.N. 

R.  E. 

20 

21 

9 

20 

21 

9 

25 

21 

9 

28 

21 

9 

29 

21 

9 

35 

21 

9 

36 

21 

9 

36 

21 

9 

36 

21 

9 

3 

20 

9 

5 

20 

10 

29 

21 

10 

30 

21 

10 

30 

21 

10 

31 

21 

10 

Total    depth 
Feet 


50 

60 

65 

37 

48 

45 

100 

110 

102 

60 

135 

100 

140 

105 

50 


an  average  of  3.9  feet  of  soil  and  leached  loess-like  silt  over  1.3  feet  of 
leached  till.  In  contrast  with  this,  24  borings  in  the  area  of  Illinoian  drift 
immediately  to  the  north  and  west,  which  succeeded  in  passing  through  the 
loess  and  into  the  leached  till  beneath,  gave  an  average  of  5.6  feet  of  soil 
and  leached  loess  or  loess-like  silt,  and  5  feet  of  leached  till,  totaling  10. 6 
feet.  The  borings  were  made  on  flat  spots  or  surfaces  so  gently  undulat- 
ing that  surface  wash  would  be  a  negligible  factor. 

2.     In  the  younger  drift  area,  in  cases  where  the  loess  is  thick  enough 
so  that  the  base  is  calcareous  and  till  was  encountered  below,  the  till  showed 


41 A  summary  of  the  data  for  northwestern  Illinois  is  given  by  Dr.  M.  M. 
Leighton,  in  Journal  of  Geology,  vol.  31,  265-281,  192:?,  but  specific  data  on  this  area 
were    contributed    by    him    from    his    field    notes. 


ILLINOIAN   AND   IOWAN     (?)    TILLS  71 

no  leaching  but  contained  limestone  pebbles  to  the  top.  This  of  course 
proves  that  deposition  of  the  drift  was  followed  immediately  by  deposition 
of  the  loess.  North  of  the  margin  of  the  ridge,  on  the  Illinoian  plain, 
several  widely  separated  borings  revealed  an  old  soil  or  humus  muck  sep- 
arating the  unweathered  loess  from  the  weathered  till.  In  other  places,  an 
old,  brown,  loess-like  silt,  2  to  3  feet  thick,  non-calcareous  and  containing 
manganese  pellets,  was  also  found  beneath  the  yellow  loess  and  on  the  un- 
derlying Illinoian  till,  but  was  not  encountered  in  the  area  of  shallow 
leaching. 

3.  The  ridge  which  bounds  the  younger  drift  area  is  gently  undu- 
lating and  has  a  glacial  contour,  and  while  not  of  great  relief  like  the  Bloom- 
ington  moraine  to  the  east  and  south,  it  is  high  enough  to  be  shown  on  the 
topographic  map  with  a  20-foot  contour.  The  average  height  of  the  ridge 
is  about  30  feet.  It  is  composed  primarily  of  till,  although  some  gravel 
deposits  occur,  as  in  the  west  half  of  sec.  4,  Marion  Township  (T.  20  N., 
R.  9  E.).  Boulders  are  fairly  numerous  south  of  the  Kelley  School,  but 
elsewhere  the  mantle  of  loess-like  silt  seems  to  be  sufficient  to  cover  them. 
A  low  terrace  of  sandy  gravel  occurs  along  Fivemile  Branch  about  half 
a  mile  south  of  the  Kelley  School,  but  elsewhere  there  is  but  little  evi- 
dence of  outwash  which  is  in  keeping  with  the  absence  of  kames.  The 
amount  of  erosion  shown  by  the  ridge  is  small. 

Earlier  workers42  mapped  the  drift  of  most  of  this  quadrangle  as 
Iowan,  with  less  than  a  square  mile  of  Illinoian  till  exposed  in  the  ex- 
treme northwest  corner  of  the  quadrangle.  The  Iowan  drift  was  de- 
scribed as  overlying  the  Illinoian  in  many  hills.  Railroad  cuts  were  noted 
where  Leverett  believed  the  Iowan  was  superimposed  on  Illinoian  till.  In 
a  later  publication,  Leverett43  mapped  all  the  Dixon  area  as  Illinoian.  That 
map  was  generalized  and  the  glacial  history  of  the  Dixon  area  was  not 
germane  to  the  discussion,  so  that  possibly  it  was  not  intended  to  classify 
all  the  drift  of  this  area  as  Illinoian.  In  1922,  he44  reaffirmed  his  earlier 
differentiation  of  the  two  tills. 

After  a  careful  study  of  the  field  evidence,  the  writer  believes  that  the 
till  in  the  central  and  northern  parts  of  the  area,  which  Leverett  and 
Hershey  differentiated  into  Illinoian  and  Iowan,  is  actually  all  contempora- 


42  Leverett,  Frank,  The  Illinois  glacial  lobe:  U.  S.  Geol.  Survey  Mon.  38,  pp. 
131-139,  1899.  O.  H.  Hershey  is  cited  as  first  making  the  differentiation,  but  no 
reference   is   given. 

43  Leverett,  Frank,  The  Pleistocene  of  Indiana  and  Michigan:  U.  S.  Geol.  Sur- 
vey   Mon.    53,    pi.    5,    1915. 

44  Leverett,  Frank,  Discussion  of  paper  by  M.  M.  Leightcn,  Further  data  on  the 
differentiation  of  the  glacial  drift  sheets  of  northern  Illinois:  Bull.  Geol.  Soc.  Amor., 
vol.   33,  p.   116,   1922. 


72  DIXON    QUADRANGLE 

neons,    and   is   of    Illinoian   age.      The   reasons    for   this    conclusion   are   as 
follows  : 

1.  Both  the  supposedly  Illinoian  and  Iowan  tills  of  Leverett  and 
Hershey  are  covered  by  loess,  which  they  regarded  as  Iowan.  In  each  case, 
the  till  beneath  the  loess  is  leached  to  an  average  depth  of  five  feet  and 
oxidized  to  about  ten  feet,  even  where  the  base  of  the  loess  is  calcareous. 
If  the  loess  is  Iowan  and  covers  Iowan  till,  the  till  should  not  be  greatly 
weathered  beneath  any  calcareous  loess,  but  the  Illinoian  till  should  show 
marked  weathering.  If  the  loess  is  Early  Wisconsin,  the  Iowan  till  should 
be  much  less  weathered  than  the  Illinoian.  As  stated  above,  there  is  no 
difference  in  the  amount  of   weathering  of  the  supposedly  distinct  tills. 

2.  The  erosion-cycle  age  of  the  Iowan  should  be  less  than  that  of  the 
Illinoian.  Instead  of  being  more  maturely  dissected  than  the  Iowan.  as  it 
should  be  under  Leverett's  hypothesis,  his  Illinoian  till  is  less  eroded.  Con- 
sidering the  greater  distance  of  the  Illinoian  till  of  Leverett  from  the 
Rock  River,  it  ought  to  show  less  erosion,  if.  as  the  present  writer  be- 
lieves, the  two  till  deposits  are  contemporaneous. 

3.  Leverett  reported  exposures  which  he  regarded  as  showing  two 
tills  in  cuts  along  the  Chicago  and  Northwestern  Railwav  in  Dixon  and 
along  the  Chicago,  Burlington  and  Ouincy  Railroad  east  of  Stratford. 
The  present  writer  was  unable  to  confirm  this  observation.  In  addition 
to  study  of  the  exposures,  trenches  were  cut  with  a  spade  through  the  sod 
and  slumped  material  to  the  original,  undisturbed,  glacial  deposits  in  each 
cut.  Augur  borings  were  also  made  at  these  cuts,  and  like  the  trenches, 
showed  weathered  loess,  fresh  loess,  leached  and  oxidized  till,  fresh  till, 
and  solid  rock,  in  most  instances.  In  two  cuts  there  is  no  calcareous  loess ; 
m  one.  the  loess  lies  directly  on  the  Galena  limestone.  Waste  from  the 
cuts  overlies  the  loess  in  several  places,  but  is  readily  recognized  as  arti- 
ficially deposited,  by  the  absence  of  a  soil  and  weathered  zone  at  the  top. 

L  Gumbotil  occurs  on  a  fiat  till  plain  in  the  southeast  corner  of  the 
XE.  %  sec.  14.  T.  21  X..  R.  10  E..  and  has  been  found  by  M.  M.  Leighton 
at  a  number  of  points  east  and  northeast  of  this  quadrangle  within  Lever- 
ett's "Iowan"  area.  Gumbotil  is  a  fine,  sticky  or  gummy  gray  clay, 
practicallv  free  from  pebbles,  which  forms  on  the  surface  of  the  till  under 
extreme  weathering.  It  is  characteristic  of  the  Illinoian  till  surface,  but 
has  not  been  reported  on  the  Iowan.  Presence  of  gumbotil  does  not  prove 
that  there  is  no  Iowan  in  the  region,  but  its  repeated  presence  on  uneroded 
areas  is  difficult  to  explain  on  the  assumption  of  later  deposition  of  the 
Iowan.  Much  more  gumbotil  would  probably  be  found,  if  the  heavy  loess 
mantle  did  not  conceal  the  till  surface. 

For  these  reasons,  it  is  believed  that  the  Iowan  ice-sheet  did  not  in- 
vade the  region  here  mapped  as  Illinoian,  and  that  its  effects  in  this  area 
are  principally  confined  to  the  possible  production  of  the  loess. 


GRAND   DETOUK   ESKER  73 

On  the  other  hand,  the  age  of  the  moraine  along  the  southern  boundary 
of  the  Illinoian  area  is  not  so  definitely  determinable.  The  uncertainty 
about  this  age  is  emphasized  in  a  recent  paper.40 

The  greater  thickness  of  the  loess,  the  soil  zone  underlying  the  loess, 
and  the  deep  weathering  of  the  till  all  distinguish  the  Illinoian  till  from 
the  Iowan  (?).  The  depth  of  leaching  found  by  Leighton  was  somewhat 
less  in  this  drift  than  in  the  Iowan  deposits  of  Iowa  but  possible  differences 
in  rainfall,  drainage,  ground-water  level,  and  original  calcareous  content 
make  it  difficult  to  compare  leaching  in  such  widely  separated  areas. 

All  available  evidence  indicates  that  the  formation  of  loess  in  this 
area  was  continuous  (p.  76),  and  the  greater  thickness  of  loess  over  the 
Illinoian  till  shows  that  part  of  the  loess  deposition  preceded  the  accumu- 
lation of  the  Iowan  (?)  till.  Heavy  loess  deposition  accompanied  and  im- 
mediately followed  the  Iowan  glaciation  in  Iowa,  but  some  also  followed 
the  recognized  Early  Wisconsin  glaciation  in  Illinois.46 

GRAND    DETOUR    ESKER 

Besides  the  till  of  the  ground  moraine  just  described,  the  Illinoian 
glacier  formed  an  esker  in  Dixon  and  Nachusa  townships  as  indicated  on 
Plate  I.  In  addition  to  its  own  interest,  the  esker  is  important  because  it 
forced  Rock  River  to  the  northwest  making  the  "grand  detour"  which  gave 
its  name  to  the  neighboring  village. 

The  esker  consists  of  well- washed  sand  and  gravel  containing  pebbles 
up  to  two  inches  in  diameter.  As  is  to  be  expected  from  its  origin,  bedding 
planes  in  the  esker  were  largely  destroyed  in  the  slumping  which  followed 
the  melting  of  the  ice.  Stratification  is  preserved  in  at  least  four  places : 
in  gravel  pits  in  the  NW.  ]/A  sec.  31,  T.  22  N.,  R.  10  E.,  and  NW.  %  sec.  23, 
T.  22  N.,  R.  9  E.,  and  in  prospecting  pits  in  the  NE.  *4  sec.  25,  and  the 
NE.  )/\  sec.  36  of  the  same  township.  In  each  case,  the  bedding  planes 
dip  from  15°  to  20°  in  a  direction  varying  from  due  west  to  N.  75°  W. 
The  maximum  thickness  of  gravel  exposed  is  9  feet,  which  was  shown 
in  the  pit  in  sec.  31.     This  face  did  not  extend  to  the  bottom  of  the  gravel. 

The  esker  extends  northwest  from  the  vicinity  of  Emmert  School, 
Nachusa  Township,  paralleling  Chamberlain  Creek  on  the  northeast,  and 
terminating  on  the  Dixon-Grand  Detour  Road,  northeast  of  Bend  School, 
Dixon  Township.  It  forms  a  well-marked  ridge  in  parts  of  sees.  14,  15  and 
25,  Dixon  Township.  Between  sees.  14  and  25  it  crosses  a  high  sandstone 
hill  where  it  is  represented  only  by  scattered  gravel,  and  in  the  valley  of 
western  sec.   24,  Dixon  Township,  it  has  been  destroyed  by  erosive   work 

45  Leighton,    M.    M.,    The    differentiation    of    the    drift    sheets    of    northwestern    Illi- 
nois:   Jour.   Geology,    vol.    31,   p.   280,    1923. 

46  Cady,    G.    H.,    Geology    and    mineral    resources    of    the    Hennepin    and    La    Salle 
quadrangles:   Illinois   State   Geol.   Survey  Bull.   37,   p.    83,   1919. 


74  DIXON    QUADRANGLE 

and  later  filling  of  Rock  River  and  its  tributaries.  The  southeastern  end 
is  not  well  defined,  but  it  originates  in  a  region  of  sand  and  gravel  with 
confused  stratification  northeast  of   Nachusa. 

This  esker  makes  the  high  dam  of  gravel  blocking  a  preglacial  valley 
about  half  a  mile  wide,  and  100  feet  deep  in  the  S\Y.  Y\  sec.  14,  Dixon 
Township.  This  is  the  largest  unfilled  preglacial  valley  which  has  not  been 
reoccupied  and  reexcavated  by  a  stream.  Although  the  gravel  is  unconsoli- 
dated and  easily  eroded,  it  was  high  enough  so  that  when  drainage  was 
established  along  what  is  now  Rock  River,  the  water  flowed  around  the 
"grand  detour''  and  adopted  a  course  five  miles  longer  than  otherwise 
would  have  been  necessary.  If  the  gravel  were  removed,  a  20-foot  flood 
today  would  send  water  through  the  old  channel. 

LOESS 

Lithology.  The  loess  of  this  area  consists  of  mineral  and  rock  par- 
ticles intermediate  in  size  between  sand  and  clay.  Except  in  the  coarser 
material,  the  naked  eye  cannot  distinguish  individual  grains.  Uniformity  in 
composition,  color  and  size  of  grain  characterizes  the  loess.  It  generally 
has  no  bedding,  and  the  only  structure  is  a  vertical  parting,  which  is 
due  to  the  fact  that  the  silt  enclosed  vertical  plant  stems  as  it  accumulated 
or  which  has  developed  on  drying  faces.  Because  of  this  parting,  the  loess 
stands  for  many  years  in  vertical  cliffs  without  serious  slumping  or  crum- 
bling. Scattered  fossils  are  found  in  the  loess  which  were  buried  in  the 
accumulating  silt.  Roughly  ellipsoidal  calcareous  concretions,  formed  by 
circulating  ground  water,  have  grown  in  the  loess  to  a  maximum  diameter 
of  an  inch. 

Where  fresh,  the  loess  is  blue-gray  and  so  highly  calcareous  that  a  drop 
of  hydrochloric  acid  causes  the  surface  to  swell  and  puff  up  sharply  as  the 
carbon  dioxide  gas  escapes.  On  exposure,  the  iron  content  is  oxidized  and 
the  carbonates  leached  out,  leaving  a  buff  to  yellow-brown,  sticky,  plastic, 
fine-grained  clay,  similar  to  the  residual  soil  from  a  limestone.  Leached 
loess  in  this  area  differs  from  limestone  soils  chiefly  in  its  large  content  of 
quartz  fragments.  Oxidation  and  leaching  of  the  loess  extend  five  to  six 
feet  below  the  surface  on  uplands  ;  where  erosion  has  occurred,  the  present 
depth  of  leaching  naturally  is  less. 

Loess  has  been  regarded  as  a  silt,  blown  from  desert  areas,  from  flood- 
plains  of  streams  carrying  their  normal  load  or  burdened  with  out- 
wash  from  glaciers,  or  from  glacial-till  areas  recently  uncovered  by 
a  retreating  glacier;  as  an  outwash  product  of  a  glacier  which  settled  in 
standing  or  slowly  running  water,  or  as  a  product  of  earthworms.  Each 
suggested  process  has  undoubtedly  produced  loess  in  some  places.  In  this 
quadrangle,   the   loess   is   a    rock   Hour    formed   by   crushing   limestones   and 


shales  with  lesser  amounts  of  sandstone  and  crystalline  rocks.  The  silt 
has  not  resulted  from  weathering  or  attrition  by  wind  or  running  water. 
Glaciers  supplied  the  material,  and  it  must  have  been  spread  over  the  up- 
lands by  the  wind,  for  some  of  the  grains  show  a  slight  rounding  off  of 
points  and  edges,  such  as  would  result  from  wind  transportation.  There 
is  no  evidence  of  lakes  from  which  the  material  could  settle,  no  elevated 
land  to  furnish  shores  for  the  lakes,  and  none  of  the  lamination  which  lake 
clays  commonly  show.  Streams  that  flooded  this  area  and  deposited  the 
silt  would  have  left  large  bodies  of  sand  and  gravel  intermingled  with  the 
finer  material,  and,  unless  the  general  slope  of  the  area  was  greatly  re- 
duced, the  streams  would  have  flowed  too  fast  to  deposit  the  loess.  Earth- 
worms bring  much  fine  material  to  the  surface,  but  they  seem  quantitatively 
incapable  of  producing  so  thick  a  body,  since  their  operations  are  chiefly 
confined  to  the  two  or  three  feet  of  soil  immediately  below  the  surface.  In 
addition,  the  underlying  till  is  deeply  weathered,  while  the  overlying  loess, 
where  thick,  is  calcareous  and  unoxidized.  No  source  for  the  loess  is  ap- 
parent in  the  subjacent  till.  The  upland  loess  is  accordingly  believed  to  be 
eolian,  although  some  of  the  loess  on  the  lower  slopes  of  valleys  may  be  a 
product  of  slope-wash  from  the  main  body  above. 

Topographic  expression.  The  loess  mantles  the  till  and  has  probably 
softened  its  contour  considerably.  Loess  areas  are  notably  smooth  or  very 
gently  rolling.  Along  roadsides  and  other  excavations,  the  loess  stands  in 
vertical  faces,  but  similar  natural  exposures  are  found  only  where  erosion 
is  rapid,  as  on  the  outside  of  curves  of  upland  streams. 

Thickness.  The  average  thickness  of  loess  in  this  area  is  about  six  feet, 
but  it  is  known  to  reach  a  maximum  of  15  feet  in  the  cement  quarry  north- 
east of  Dixon.  The  loess  seems  somewhat  thicker  immediately  east  of  Rock 
River,  than  either  west  of  the  river  or  several  miles  east.  Undissected  loess- 
ial  areas  west  of  the  river  are  so  limited  that  this  suggestion  cannot  be 
tested  by  enough  measurements  to  prove  it. 

Area.  Loess  overlies  all  the  undissected,  till-covered  area  and  also 
covers  some  rock  in  the  uplands  where  till  is  missing.  Where  vigorous 
erosion  is  now  in  progress,  there  is  little  loess  on  the  lower  slopes,  but  in 
older  valleys,  loess  mantles  the  slopes  and  sometimes  the  flood-plain.  Some 
of  this  loess  has  been  deposited  by  the  wind  since  the  valleys  were  formed  ; 
but  probably  more  of  it  has  been  contributed  by  creep  and  slope-wash  from 
the  uplands. 

Age.  Loess  is  accumulating  to  a  slight  extent  in  this  area  today,  but 
by  far  the  greater  part  of  the  Mississippi  Valley  loess  is  either  late  Iowan 
and  early  Peorian,  or  Early  Wisconsin.  Before  the  loess  was  deposited,  the 
Illinoian  till  was  leached  to  an  average  depth  of  live  feet,  which  is  practical- 


76  DIXON    QUADRANGLE 

ly  the  amount  of  leaching  of  the  Iowan  (  ?)  till  and  its  overlying  loess  to- 
gether. 

Since  the  loess  on  the  Illinoian  till  is  not  separable  into  older  and 
younger  portions,  it  must  have  been  deposited  without  any  interruption 
which  permitted  important  weathering ;  also  since  loess  overlies  the  Iowan  (?) 
till,  which  is  unweathered  where  the  base  of  the  loess  is  calcareous,  loess 
deposition  must  have  followed  immediately  after  the  retreat  of  the  Iowan  (?) 
ice-sheet.  So  far  as  the  Dixon  area  supplies  evidence,  the  loess  could 
be  entirely  of  Iowan  and  early  Peorian  age.  This  is  in  accord  with  the 
evidence  in  nearby  areas.  Thick  loess  deposits  underlie  the  Early  Wis- 
consin till  in  Bureau  County,47  25  miles  south  of  the  quadrangle.  At  a  point 
17  miles  northeast  of  this  area,  Leighton48  has  described  thrusting  of  a  rock 
ledge  by  the  Early  Wisconsin  ice-sheet  over  fossiliferous  loess. 

After  a  study  of  the  relations  of  the  loess  to  the  Iowan  drift  in  north- 
eastern Iowa,  Alden  and  Leighton49  concluded  that  the  great  bulk  of  the 
loess  in  that  state  is  early  Peorian  in  age,  although  some  was  probably  de- 
posited during  the  closing  stages  of  the  Iowan.  The  evidence  for  the  inter- 
glacial  date  is  the  existence  of  fossil  land-snail  shells  in  the  loess,  which 
Shimek  has  found  are  chiefly  the  species  that  live  in  the  climate  prevailing 
today  in  the  Upper  Mississippi  Valley  region. 

EARLY     WISCONSIN     VALLEY     TRAIN 

A  fairly  well-developed  valley  train  of  Early  Wisconsin  age  fills  Kyte 
River  valley.  Much  material  of  the  same  age  is  undoubtedly  present  in 
the  valley  train  of  Rock  River,  but  it  is  not  separable  from  the  Late  Wiscon- 
sin valley  train.  When  the  Early  Wisconsin  glacier  reached  its  maximum 
development,  its  terminus  in  Kyte  Valley  was  about  10  miles  east  of  this 
quadrangle.  Water  from  the  melting  ice  carried  well-washed  sand  and 
gravel  into  the  river.  Overloaded,  the  river  filled  its  valley  18  feet  above  the 
present  stream  level  with  clean,  sharp  sand,  angular  gravel  and  rounded 
pebbles  ranging  up  to  two  inches  in  diameter.  All  kinds  of  rock  are  repre- 
sented in  the  filling,  but  limestone  predominates. 

Kyte  River  has  removed  about  35  per  cent  of  the  train  which  originally 
stood  above  the  present  stream  level.  No  information  as  to  the  depth  of 
the  filling  is  available,  but  it  probably  extends  60  to  75  feet  below  the  river 
level,  just  as  does  the  gravel  under  Rock  River.  The  remainder  of  the 
valley  train  forms  high,  well-drained,  fertile  terraces  along  the  length  of 
the  river  in  this  quadrangle.      (See  Plate  I.) 


47  Leverett,    Prank,    The    Illinois   glacial   lobe:    U.    S.    Geol.    Survey    Mon.    38,    p.    187, 
1899. 

48  Leighton,    M.    M.,    in   Bretz,    J   H.,    Geology   and   mineral   resources   of   the   Kings 
quadrangle:   Illinois  State  Geol.  Survey  Bull.  43,  pp.  239-241,   1923. 

49  Alden,    W.    C.,   and   Leighton,    M.    M.,    The    Iowan    drift:    Iowa   Geol.    Survey,    vol. 
2G,    p.    158,    1917. 


EARLY  AND  LATE  WISCONSIN  VALLEY  TRAINS  77 

LATE  WISCONSIN  VALLEY  TRAIN 

The  Green  Bay  lobe  of  the  Late  Wisconsin  ice-sheet  overran  the  divide 
between  Green  Bay  and  Rock  River  basins  and  advanced  southwestward  to 
Janesville,  Wisconsin.  Water  from  the  melting  ice  swept  u  tremendous 
quantity  of  sand  and  gravel  into  Rock  River.  This  filled  the  channel,  raised 
the  river  level  and  finally  filled  the  entire  valley  with  well-washed,  roughly 
stratified  sand  and  gravel.  A  similar  valley  train  forming  in  Mississippi 
River  tended  to  pond  Rock  River,  causing  still  further  deposition,  until  the 
channel  of  the  Rock  was  aggraded  to  the  level  of  the  Mississippi. 

The  valley  train  consists  chiefly  of  sand,  with  less  than  15  per  cent  of 
gravel  over  one-fourth  inch  in  diameter.  Some  pits  have  no  gravel,  but 
most  exposures  contain  flat-topped  lenses  of  gravel,  ranging  up  to  three 
inches  in  diameter.  The  sand  is  very  clean  and  fairly  sharp.  The  grains 
that  are  rounded  are  either  limestone  or  else  the  "frosted"  sand  from  St. 
Peter  or  lower  sandstones.  All  the  gravel  is  rounded,  as  is  natural  after 
being  rolled  more  than  50  miles.  Limestone  pebbles  are  most  abundant  in 
spite  of  their  softness,  for  probably  98  per  cent  of  the  original  gravel  was 
limestone,  and  much  of  it  has  not  yet  been  crushed  and  eliminated  by  trans- 
portation. In  spite  of  its  porosity  and  susceptibility  to  weathering,  at  no 
place  is  the  valley  filling  leached  and  oxidized  to  a  greater  depth  than  two 
feet. 

The  following  section  is  typical  of  the  valley  train,  although  probably 
none  of  its  members  continues  for  a  quarter  of  a  mile. 

Section  of  a  gravel  %>it  in  West  Dixon  in  the   SW.   %   NE.   %   sec.   6,   T.   21  N., 

R.  9  E. 

Description  of  strata  Thickness 

Feet 

Dune  sand  and  loam 

Sand,  with  some  interbedded  gravel. 12 

Sand,  0.05  to  2  mm.  in  diameter;   thin,  nearly  horizontal  laminations..  6 

Gravel  and  sand,  up  to  one  inch  in  diameter 10 

Sand,  0.5  to  1.0  mm.,  with  thin,  perfect  cross  beds  dipping  12°  SW 7 

Gravel  and  sand,  up  to  1.5  inches  in  diameter;   bedding  indistinct 8 

River  level    

Total     43 

Like  the  Early  Wisconsin  valley  train  in  Kyte  River,  this  filling  forms 
high,  dry,  prominent  terraces  which  extend  along  the  entire  course  of  Rock- 
River  through  this  quadrangle.  Originally,  the  surface  of  the  train  must 
have  been  nearly  flat,  but  Rock  River  in  removing  it  has  sculptured  it  into 
many  terraces.  (See  p.  16  and  fig.  1.)  The  terraces  are  not  systematic, 
but  represent  purely  accidental  interruptions  in  the  side-swings  of  the  en- 
trenching river.  As  shown  on  Plate  I,  the  valley  train  has  an  average  width 
of  half  a  mile  across  the  quadrangle. 


78  DIXON    QUADKANGLE 

Originally,  the  valley  was  filled  about  45  feet  above  present  stream 
level.  Depth  of  sand  and  gravel  below  the  stream  is  uncertain.  Several 
holes  drilled  just  below  the  Illinois  Central  bridge  in  Dixon  penetrated  more 
than  60  feet  of  sand  and  gravel,  indicating  a  total  thickness  for  the  original 
train  of  approximately  105  feet,  if  these  test  holes  were  located  in  the  form- 
er main  channel. 

BACKWATER    DEPOSITS 

Deposits  of  alluvium  of  local  origin  formed  in  valleys  tributary  to 
Rock  River  as  a  result  of  the  growing  valley  train.  Just  as  Rock  River 
had  to  aggrade  its  channel  as  fast  as  Mississippi  River  filled  its  valley, 
so  Pine,  Chamberlain  and  Franklin  creeks  were  forced  to  raise  their  beds 
in  order  to  flow  into  the  Rock.  Consequently,  these  creeks  deposited  sedi- 
ment in  their  upper  courses  and  gradually  built  up  to  the  level  of  Rock 
River.  It  is  probable  that  their  lower  courses  were  temporarily  ponded 
and  that  delta  deposits  from  Rock  River  extended  up  into  these  streams, 
for  cross-bedding  dipping  upstream  is  exposed  along  Pine  Creek  in  a  ter- 
race north  of  the  farm  house  in  the  NE.  %  SE.  Y^  sec.  3,  Grand  Detour 
Township.  A  similar  situation  exists  near  the  southwest  corner  of  sec. 
24,  Dixon  Township.  The  backwater  deposits  are  well-bedded  sand,  car- 
bonaceous silt  and  clay,  and  they  now  form  distinct  terraces  above  the 
present  alluvium.  A  similar  deposit  resulting  from  the  Early  Wisconsin 
filling  of  Kyte  River  is  found  along  the  unnamed  stream  in  sec.  30,  Pine 
Rock  Township. 

RECENT    SEDIMENTS 
FLOOD-PLAIN    ALLUVIUM 

All  permanent  streams  in  this  area  have  alluvial  flood-plains  on  which 
they  deposit  their  surplus  load  in  flood  time.  During  low  water,  the  stream 
follows  a  channel  a  few  feet  below  the  level  of  the  alluvium.  This  al- 
luvium has  been  deposited  in  greatly  increased  quantities  within  the  last  75 
years.  As  a  result  of  the  breaking  of  the  prairie  sod,  rain  water  runs 
away  more  quickly  over  the  surface  and  can  erode  the  soil  more  vigorously 
than  before.  In  deep  stream  channels  in  the  alluvium,  a  zone  of  very 
black,  carbonaceous  silt  can  be  seen  one  to  three  feet  below  the  present 
surface.  Above  this,  the  silt  is  uniformly  lighter  in  color,  usually  more 
sandy,  and  often  laminated  with  several  black  soil  zones.  The  surface  al- 
luvium, similarly,  is  lighter  in  color  than  this  distinctive  lower  horizon 
which  marks  the  alluvial  surface  before  agriculture  commenced  in  this 
region. 

PEAT    AND    MUCK 

In  the  lower  courses  of  Kyte  River  and  Franklin  Creek,  peat  and 
vegetable  muck  are  accumulating  over  considerable  areas,  as  shown  on 
Plate   I,    gradually    filling    in    depressions    which    formed    behind    the    Rock 


RECENT    DEPOSITS  79 

River  valley  train.  Backwater  deposits  did  not  fill  these  depressions  and 
the  sluggish  streams  bring  in  little  sediment.  The  slow  process  of  vegetal 
deposition  is  destroying  these  marshes  and  forming  exceedingly  rich  farm 
land. 

SAND     DUNES 

Small  sand-dune  areas  are  indicated  on  Plate  I  in  sees.  27  and  33, 
T.  21  N.,  R.  10  E.,  and  along  Rock  River  in  sees.  21  and  22,  Dixon 
Township,  sees.  11,  12  and  13,  Grand  Detour  Township,  sees.  5,  6  and  7, 
Taylor  Township  and  sees.  20  and  21,  Nashua  Township. 

The  dunes  near  Temperance  Hill  School  (T.  21  N.,  R.  10  E.)  have 
formed  on  the  sandy  surface  of  the  Iowan  (  ?)  till.  Other  dunes  nearby  are 
too  small  to  be  indicated  on  the  map.  The  north  side  of  the  dune  area 
in  sec.  33  has  been  overpastured,  vegetation  has  been  destroyed,  and  some 
sand  moves  during  high  winds.     With  this  exception,  the  dunes  are  dead. 

The  dunes  along  Rock  River  are  formed  chiefly  of  sand  from  the 
valley  train  but  contain  a  much  larger  proportion  of  St.  Peter-type  sand 
grains  than  does  the  valley  filling.  Probably  they  have  received  an  ap- 
preciable addition  of  sand  from  the  St.  Peter  outcrop  upon  which  all  of 
them  rest,  except  those  in  sec.  7,  Taylor  Township. 


CHAPTER  IV— GEOLOGIC  HISTORY 
Introduction 

The  history  of  the  area  is  partly  written  in  the  rocks  described  in 
the  preceding  chapter.  Many  portions  of  the  record,  however,  are  in- 
complete, and  others  are  ambiguous  or  present  knowledge  does  not  furnish 
the  explanation  of  existing  features. 

Pre-Cambrian  Eras 

Because  no  rock  of  this  age  has  been  found  in  place  in  this  area, 
the  history  must  be  inferred  from  evidence  in  neighboring  areas.  In 
Wisconsin,  a  series  of  pre-Cambrian  sedimentary  rocks  is  known.  They 
were  intruded  by  various  igneous  rocks,  folded,  compressed,  and  metamor- 
phosed., forming  what  has  been  called  the  ''crystalline  complex'''  of  igneous 
and  metamorphic  rocks.  Upon  it  long  continued  erosion  developed  a  par- 
tial peneplain  which  has  been  traced  by  surface  exposures  and  wells  south- 
ward across  Wisconsin,  as  described  in  Chapter  III.  Presumably,  a  similar 
series  of  metamorphosed  igneous  and  sedimentary  formations  underlies  the 
Paleozoic  rocks  of  this  area.  In  northern  Wisconsin  and  northeastern  Min- 
nesota, a  series  of  Keweenawan  red  sandstones  and  shales  covers  the  crys- 
tallines, and  it  has  been  suggested  that  rocks  of  this  series  have  been  reached 
in  deep  wells  in  Dixon.  The  evidence  was  considered  in  the  last  chapter 
and  reasons  were  stated  for  believing  that,  although  Keweenawan  rocks 
may  underlie  this  area,  they  have  not  been  proved  by  any  drilling  up  to 
this  time. 

Paleozoic  Era 

CAMBRIAN  PERIOD 

The  red  color  of  the  Keweenawan  sediments  is  due  to  the  iron  oxide 
which  thev  contain  and  indicates  that  little  or  no  organic  matter  was  de- 
posited with  those  sands  and  clays.  Similarly,  the  pink  and.  in  a  few  places. 
red  color  of  some  of  the  Croixan  sands  found  in  this  area  indicates  that  the 
sand  was  deposited  with  little  included  organic  matter.  At  present,  the 
absence  of  life  and  the  red  color  seem  to  suggest  desert  conditions.  The  fact 
that  many  of  the  very  small  sand  grains  are  either  rounded  or  "frosted" 
offers  further  indication  of  their  origin  in  a  barren  area  where  wind  trans- 
portation was  dominant,  where  soft  and  cleavable  minerals  were  ground  to 
dust  and  blown  away,  and  where  hard  minerals  other  than  quartz  were  elim- 
inated by  thorough  chemical  weathering,  which,   followed  by  sorting,  pro- 

SO 


GEOLOGIC    HISTORY  81 

duced  a  pure-quartz  sand.  Some  of  the  sand  may  have  come  from  the 
crystalline  rocks  in  this  area,  but  much  of  it  was  probably  carried  from  the 
northern  Wisconsin  and  Canadian  crystalline  areas  by  southward-flowing 
streams.1 

From  the  study  of  Cambrian  deposits  in  other  areas,  it  is  known  that 
the  ocean  advanced  from  the  south  or  southeast.  As  the  shoreline  moved 
northward,  at  least  the  upper  part  of  this  well-prepared  sand  was  worked 
over,  washed  and  deposited  in  strata  on  the  ocean  floor.  At  certain  times, 
less  sand  was  laid  down,  either  because  streams  did  not  supply  it  or  be- 
cause the  water  was  too  deep  to  permit  the  waves  to  roll  it  to  this  area, 
and  the  shells  of  animals  and  calcareous  structures  of  plants  accumulated, 
forming  lime  muds.  These  lime  muds  were  changed  to  dolomite  by  sub- 
stituting magnesia  for  part  of  the  lime  either  while  still  in  the  form  of  mud 
or  after  they  had  solidified  to  limestone.  So,  with  alternating  deposition 
of  sand  and  of  carbonates,  possibly  interrupted  by  withdrawal  of  the  sea 
and  exposure  to  the  air,  more  than  1480  feet  of  sediments  accumulated  In 
the  Cambrian  sea  on  the  present  site  of  Dixon. 

ORDOVICIAN    PERIOD 

LOWER   ORDOVICIAN    OR    PRAIRIE    DU    CHIEN    EPOCH 
ONEOTA     STAGE 

According  to  the  generally  accepted  geologic  chronology,  Croixan  de- 
position was  continuous  with  that  of  the  Beekmantown  epoch  which  is  rep- 
resented in  this  area  by  the  Prairie  du  Chien.  The  ocean  water  was  clearer, 
but  not  necessarily  deeper,  and  carbonate  muds  accumulated  which  consoli- 
dated to  form  the  150  to  200  feet  of  Oneota  dolomite.  Minor  amounts  of 
sand  and  clay  were  swept  into  the  ocean  and  buried  in  the  carbonate  ac- 
cumulation. 

"NEW    RICHMOND"     STAGE 

The  "New  Richmond"  sandstone  supplies  the  first  field  evidence  from 
this  area.  Up  to  this  horizon  the  history  has  been  interpreted  from  well 
cuttings  and  from  outcrops  in  neighboring  states.  In  the  valley  of  Franklin 
Creek,  the  oldest  formation  outcropping  in  this  state  is  exposed.  Evidence 
has  already  been  summarized  which  indicates  that  this  outcrop  is  part 
of  a  bar  formed  on  the  Ordovician  ocean  floor.  The  sand  is  beauti- 
fully rounded  into  spheres  and  ellipsoids  of  limpid,  frosted  quartz.  While 
it  probably  was  polished  and  ground  up  by  wind  action  on  land,  it  clearly 
was  deposited  here  by  the  ocean.  It  is  apparently  similar  to  the  Croixan 
in  its  place  and  mode  of  origin,  and  manner  of  transportation  and  depo- 
sition, except  that  the  "New  Richmond"  is  thinner  and  less  continuous. 


1  Dake,   C.    L..,   The   problem   of   the   St.   Peter   sandstone:    Missouri   Sch.    Mines   and 
Met.  Bull.,  vol.  6,  No.   1,  pp.  216-218,   1921. 


82  DIXON    QUADRANGLE 

The  coming  of  this  sand  may  have  been  due  (1)  to  an  uplift  of  the 
land  to  the  north,  which  enabled  the  faster  flowing  streams  to  carry  sand 
into  the  ocean,  (2)  to  an  uplift  of  the  ocean  floor,  permitting  the  waves 
to  wash  the  bottom  and  roll  sand  to  this  area,  (3)  to  the  shifting  of  the 
mouth  of  a  stream  pouring  sand  into  the  ocean  at  a  new  location,  or  (4) 
to  some  change  in  general  wind  direction  which  either  blew  sand  to  the 
ocean  or,  by  shifting  the  shore  currents,  changed  the  site  of  sand  deposi- 
tion. In  the  absence  of  good  exposures  over  a  large  area  to  the  north, 
these  possibilities  cannot  be  investigated  and  the  changes  which  actually 
took  place  cannot  be  determined. 

In  all  probability  the  "New  Richmond''  simply  represents  a  sandy 
phase  of  the  Shakopee  deposition.  The  bedding  of  the  sandstone  and 
limestone  is  conformable  wherever  the  contact  is  exposed  in  this  or  neigh- 
boring states.  At  many  places,  the  "New  Richmond"  is  missing  and  the 
Shakopee  and  Oneota  unite.  No  evidence  of  erosion  has  been  reported  from 
such  places,  and  the  absence  of  the  "New  Richmond"  indicates  that  no 
sand  deposits  interrupted  the  formation  of  the  more  common  carbonate 
and  argillaceous  muds. 

SHAKOPEE     STAGE 

The  Shakopee  ocean  was  very  shallow.  Waves  molded  the  muds  into 
ripple  marks.  Fresh,  soft  sediments  were  repeatedly  exposed  to  the  air 
by  low  tides  or  oscillations  of  the  ocean  level.  Upon  drying  out,  the  lime- 
stone checked  and  cracked  open.  The  following  mud  layer  not  only  cov- 
ered the  surface,  but  settled  down  in  the  cracks  and  preserved  their  record. 

The  thin-bedded,  shaly  limestones  or  dolomites  solidified  quickly  and 
in  many  places  were  broken  and  disarranged  before  the  overlying  beds 
formed.  What  caused  the  crumpling  that  formed  these  "edgewise  con- 
glomerates" ?  Possibly  cryptozoon  reefs  expanded  too  widely,  became 
unstable  and  collapsed.  Fragments  of  the  algae  commonly  occur  in  the 
brecciated  masses.  Possibly  dolomitization  caused  shrinkage  and  collapse 
of  underlying  layers.  Wave  action  is  not  a  probable  explanation,  for 
the  breccia  is  not  sorted,  wave-worn  or  arranged  in  horizontal  layers. 
Higher  beds  extend  over  the  irregular  masses  and  follow  their  outlines 
without  fracturing,  proving  that  these  brecciated  masses  were  formed 
during  Shakopee  deposition. 

The  ocean  was  usually  muddy.  Clay  settled  with  the  animal  structures, 
making  all  the  dolomite  very  argillaceous.  Sand  was  probably  supplied 
from  the  same  source  as  that  of  the  "New  Richmond",  and  sand  grains 
were  freely  embedded  in  the  muds  or  spread  out  in  thin  layers  over  the 
ocean  floor.  Conditions  varied  from  place  to  place  so  that  pure  clay  was 
deposited  near  an  area  where  more  agitated  water  was  spreading  sand  over 


GEOLOGIC    HISTORY  83 

the  bottom.  As  a  consequence,  individual  beds  cannot  be  traced  long  dis- 
tances  and  neighboring  sections   can  be   correlated  only   in  general   terms. 

At  times,  clay  was  deposited  so  rapidly  that  no  organic  matter  ac- 
cumulated with  it.  Red  and  purple  shales  formed  where  the  well-weathered, 
red,  yellow  or  brown  soil  from  the  land  areas  was  deposited  by  the  ocean. 
When  accumulation  was  less  rapid,  enough  plant  and  possibly  animal  mat- 
ter was  buried  in  the  clay  to  react  with  its  iron  content  and  produce  a  blue, 
green  or  gray  color.  All  the  calcareous  and  fossiliferous  strata  originally 
contained  enough  organic  matter  to  reduce  the  iron  and  to  yield  a  light- 
colored  rock.  Gastropods,  of  which  the  snails  are  modern  examples,  crawled 
on  the  bottom,  while  peculiar  calcareous  algae  built  the  laminated,  hemi- 
spherical masses  which  were  long  so  little  understood  that  they  received 
the  name,  Cryptozoon,  meaning  "hidden  animal."  There  were  other  plants 
which  left  the  twig-like  fucoids  as  their  record,  and  worms  burrowed 
through  the  mud. 

All  the  chemical  sediment  of  the  Shakopee  is  dolomite.  The  usual 
origin  of  dolomite  is  the  substitution  of  magnesia  for  part  of  the  lime  in  un- 
consolidated sediments  that  otherwise  would  have  formed  limestone.  The 
alteration  of  the  Shakopee  to  dolomite  was  completed  as  deposition  occurred. 
No  evidence  of  later  alteration,  such  as  irregular  or  high  porosity,  solution 
channels  or  cavities,  or  especially  thorough  dolomitization  along  bedding 
or  joint  planes,  is  found  in  the  fresh  rock.  The  evidence  is  unusually  clear 
in  the  brecciated  masses,  where  the  fragments  are  dolomite  and  are  sharply 
separable  from  the  enclosing  dolomite  matrix.  If  alteration  followed  the 
slumping,  a  blending  of  the  materials  and  blurring  of  the  contact  would 
have  resulted.  The  upper  Shakopee  was  deposited  after  conditions  became 
more  stable,  when  the  ocean  was  clearer,  and  less  clastic  sediment  was 
accumulating.  The  thick,  uniform  beds  of  pure  dolomite  of  the  Clear  Creek 
basin  (sees.  4  and  9,  Taylor  Township)  are  typical  of  the  sediments  formed 
at  that  time. 

Then  the  ocean  withdrew.  Deep  erosion  and  slumping  or  folding 
of  the  Shakopee  followed.  Exposures  are  too  limited  to  determine  the 
amount  and  extent  of  the  folding.  All  of  the  folds  and  steep  dips  exposed 
could  have  resulted  from  slumping  of  the  partially  consolidated,  deeply- 
eroded  sediments.  Such,  for  instance,  might  have  been  the  origin  of  the 
little  syncline  shown  in  fig.  10.  The  anticline  shown  in  fig.  11  has  a 
dip  of  45°  on  one  limb  while  the  other  limb  is  flat.  This  dip  is  not  dupli- 
cated in  any  of  the  outcrops  in  the  vicinity.  Shattering  of  the  limestone 
without  bending  and  the  absence  of  slickensides  indicate  that  the  folding- 
was  accomplished  under  very  slight  cover.  There  is  no  parallelism  be- 
tween the  attitudes  of  strata  in  adjacent  exposures.  Several  nearby  out- 
crops show  irregular  variations  in  dip  similar  to  that  of  fig.   10.     Appar- 


84 


DIXOX    QUADRANGLE 


ently,  the  steep  dip  is  purely  local.  The  longest  outcrop  showing  steep  dip 
is  located  about  a  mile  southeast  of  the  National  Silica  Company's  plant, 
in  a  ravine  in  sec.  9,  T.  23  N.,  R.  10  E.,  where  a  well-defined  bed  dips  12° 
NE.  throughout  an  exposure  about  120  feet  long.  There  are  no  Shakopee 
outcrops  within  half  a  mile  with  which  to  compare  this  unusual  attitude. 
The  two  examples  last  cited  have  been  described  because  thev  are  the 
only  cases  where  the  slump  origin  of  the  distortion  seems  at  all  doubtful. 
The  writer  believes  that  the  deformation  of  Shakopee  sediments  is  entirely 
a  local  and  surface  feature  and  without  diastrophic  implications,  because 
(1)  there  is  no  system  in  the  attitudes  of  various  outcrops,  (2)  the  folds 
cannot  be  traced  from  one  outcrop  to  another,  (3)  the -bulk  of  the  out- 
crops show  practically  horizontal  strata,  which  would  be  improbable  if 
regional  folding  had  crumpled  some  beds,  (-1)  close  folding  of  the  Shakopee 
has  not  been  found  in  any  other  area,   (5)   the  formation  is  shown  by  its 


Fig.  10.    Gentle  folding  of  the  Shakopee  dolomite,  NE.   V±   NE.   V±   sec.   33, 

T.  22  N,  R.  10  E. 


contemporaneous  edgewise  conglomerate  to  have  been  very  unstable,  and  (6) 
the  deep  erosion  with  steep  cliffs  favored  such  slumping. 

Valleys  at  least  65  feet  deep  were  cut  in  the  Shakopee.  Xo  cliffs 
are  recognizable,  but  in  two  places  in  sec.  30,  Oregon  Township,  outcrops 
prove  that  the  contact  slope  must  exceed  25°.  Similarly,  exposures  in 
ravines  on  the  west  side  of  Clear  Creek  in  sec.  4,  T.  22  N.,  R.  10  E.  prove 
a  dip  exceeding  20°.  Contacts  are  poorly  exposed  because  of  slumping 
down  of  the  St.  Peter  and  because  the  sandstone  is  easily  stripped  away 
where  the  contact  is  unprotected. 

Where  the  St.  Peter  rests  on  the  Shakopee  there  is  no  evidence  of 
residual  soil  or  weathered  chert,  such  as  have  been  found  in  other  areas. 
In  Franklin  Creek  a  green  clay  lies  at  the  contact,  but  it  probably  repre- 
sents post-St.  Peter  leaching  of  the  dolomite,  for  it  is  not  oxidized,  does 
not  grade  up  into  the  sandstone,  is  not  granular  as  many  residual  soils  are. 


GEOLOGIC    HISTOKY  85 

and  analogous  clays  follow  joints  and  bedding  planes  deep  below  the  zone 
of  oxidation  in  the  Shakopee  and  Platteville  today.  A  few  fresh,  angu- 
lar chert  and  rare  dolomite  fragments  are  found  in  the  St.  Peter  within  50 
feet  of  the  steep  Shakopee  contacts,  indicating  that  erosion  was  proceeding 
under  water  while  the  St.  Peter  was  accumulating. 


Fig.  11.  Sharp  folding  and  fracturing  of 
the  Shakopee  dolomite,  300  feet  east  of 
fold  shown  in  fig.  10.  (Photograph  by 
G.  H.  Cady.) 

MIDDLE  ORDOVICIAN  EPOCH 
ST.     PETER    STAGE 

Following  the  erosion  just  described,  the  sea  returned,  advancing  from 
the  south  over  this  surface  of  comparatively  high  relief,  and  the  St.  Peter 
sandstone  was  deposited  on  the  ocean  floor. 

Grabau2   believed  that  the  lower   St.   Peter  was  deposited   during  the 


2  Grabau,   A.    W.,    Types    of   sedimentary    overlap:    Bull.    Geol.    Soc.    Amer.,    vol.    17, 
p.   618,  1905. 


S6  DIXOX    QUADRANGLE 

withdrawal,  or  regression,  of  the  ocean  which  closed  the  Prairie  du  Chien 
epoch,  and  that  the  tipper  St.  Peter  was  spread  over  the  area  in  the  absence 
of  the  water  and  during  its  return.  This  was  not  the  case  in  this  area 
or  in  adjacent  areas  in  Wisconsin,  for  dolomite  pebbles  and  fragments  would 
have  been  mingled  with  much  sand  in  the  valleys  during  the  period  of 
erosion,  and  unless  all  the  sand  were  removed  before  the  later  deposition, 
a  marked  erosional  unconformity  would  separate  early  and  late  sandstones. 
Neither  of  these  phenomena  is  present. 

Like  the  "New  Richmond"  sandstone  below,  the  St.  Peter  sand  is 
well-rounded  and  frosted,  but  is  more  uniform  in  size.  Its  purity,  rounded 
grain  and  thorough  sorting  are  due  to  wind  transportation,  but  its  bedding 
is  horizontal,  and  its  cross  beds  are  curved  and  never  dip  steeply.  Near 
the  middle  of  the  formation  (at  the  south  end  of  the  Grand  Detour  bridge). 
it  shows  oscillation  ripple  marks  which  are  formed  in  standing  water; 
it  contains  marine  worm  borings  ;  it  carries  glauconite ;  and  some  of  its 
sand  grains  are  often  '20  times  the  size  of  adjacent  grains,  which  variation 
is  much  greater  than  that  of  dune  sands.  Accordingly,  it  seems  clear 
that  while  the  St.  Peter  was  originally  a  dune  sand,  it  was  here  deposited 
under  marine  conditions.  The  advance  of  the  ocean  was  probably  from  the 
south  and  the  sand  was  washed  down  the  slope  of  the  ocean  floor  as  the 
shoreline  transgressed  northward  across  the  crystalline  rocks  which  previous- 
ly had  supplied  the  sand  for  the  Croixan  and  "New  Richmond"  strata.  Pos- 
sibly the  outcrop  of  the  Croixan  sandstone  itself  supplied  part  of  the  sand.3 

The  sand  buried  the  erosion  surface  on  the  Shakopee.  gradually  over- 
whelming the  hills  and  reaching  a  thickness  of  nearly  '200  feet  in  many 
places.  Greater  thicknesses  occur  outside  this  area  at  points  not  on  the 
La  Salle  anticline.  Where  Shakopee  hills  project  high  into  the  St.  Peter. 
the  sand  was  often  less  than  40  feet  deep. 

The  La  Salle  anticline  is  the  dominating  structure  of  northern  Illinois. 
Its  growth  began  during  St.  Peter  deposition  and  as  a  result  the  sand  thins 
down  to  less  than  40  feet  along  the  crest  of  the  structure  near  Franklin 
Creek.  Waves  swept  the  top  of  the  St.  Peter  keeping  it  practically  plane. 
Such  a  marked  reduction  in  thickness  indicates  a  corresponding  uplift,  and 
probably  the  La  Salle  anticline  had  been  raised  at  least  100  feet  before  the 
deposition  of  the  Glenwood  shale. 

GLEN  WOOD    STAGE 

The  St.  Peter  deposition  closed  with  the  influx  of  a  great  quantity  of 
green  clay  from  the  northwest.  The  thickest  described  occurrence  of  this 
clay  is  in  its  type  locality  in  northeastern  Iowa,  growing  thinner  to  the  east. 


Dake,    C.    I-..    The    problem   of   the    St.    Feter   sandstone:    Missouri    Sch.    Mines   and 
Met.    Bull.,    vol.    6,    No.    1.    p.    21S.    1921. 


GEOLOGIC    HISTORY  87 

southeast  and  south,  and  practically  disappearing  in  the  Hennepin-La  Salle 
area.  At  first  the  waves  churned  up  clay  and  sand  together,  forming  a 
transition  zone  between  the  two  formations.  As  the  Glen  wood  grew  thicker, 
storms  no  longer  agitated  the  bottom  deep  enough  to  reach  the  sand,  and 
several  feet  of  argillaceous,  green,  glauconitic  shale  were  formed.  Condi- 
tions attending  the  mud  deposition  were  apparently  most  unsuitable  for 
existing  animal  life,  or  at  least  there  was  no  fauna  in  the  region  adapted  to 
living  in  this  muddy  sea.  Since  clay  furnishes  ideal  conditions  for  the 
preservation  of  shells  and  other  structures,  it  is  improbable  they  have  since 
been  destroyed  by  solution. 

The  uplift  of  the  La  Salle  anticline  continued.  Shallow  water  above 
the  anticlinal  axis  favored  wave  work  and  prevented  deep  deposition  of  the 
clay.  A  thin  bed  of  clay  and  sand  accumulated  on  much  of  the  axis,  while 
along  the  western  limb  of  the  structure,  clay  was  laid  down  to  a  depth  of 
seven  feet  or  more,  carrying  valuable  potash  in  the  form  of  glauconite. 

PLATTEVILLE  STAGE 

The  inflow  of  Glenwood  mud  decreased  greatly  and  the  ocean  became 
clearer.  Sand  was  washed  across  the  ocean  floor  and  mingled  with  the 
argillaceous  muds.  At  first  conditions  for  fossilization  were  not  very  fa- 
vorable, and  an  argillaceous,  somewhat  sandy,  magnesian  limestone  resulted. 
Probably  the  sand  came  from  the  St.  Peter  exposure  on  the  La  Salle  anti- 
cline, since  the  grains  are  identical.  The  sandy  Buff  limestone  is  thin  and 
discontinuous  over  the  anticline  and  the  Blue  limestone  which  first  cov- 
ered the  anticline  is  not  arenaceous.  The  total  uplift  of  the  anticline  by 
this  time  probably  had  amounted  to  at  least  125  feet.  Non-deposition  and 
minor  erosion  on  the  anticline,  with  simultaneous  heavy  deposition  on  the 
adjacent  lower  parts  of  the  ocean  floor,  reduced  the  topographic  promi- 
nence of  the  anticline.  A  deficiency  of  100  feet  or  more  of  the  St.  Peter, 
of  5  feet  of  Glenwood  shale  and  of  15  feet  of  the  Buff  limestone  indicates 
part  of  the  total  movement.  There  is  no  way  to  estimate  the  elevation  of 
the  anticlinal  axis  above  the  neighboring  region,  but  probably  it  was  slight, 
since  the  overlying  beds  always  appear  conformable  with  the  Glenwood 
shale. 

The  Buff  was  partly  altered  to  dolomite  before  the  deposition  of  the 
Blue.  Like  the  Shakopee  dolomite,  it  does  not  show  shrinkage,  alteration 
along  structural  planes,  or  high  porosity.  It  was  not  dolomitized  by  water 
later  circulating  through  the  St.  Peter,  for  where  the  Glenwood  shale  is 
missing,  the  Blue  is  often  in  contact  with  the  sandstone,  and  silicification 
has  resulted,  but  not  dolomitization. 

Conditions  favorable  for  the  preservation  of  fossils,  and  probably  an 
environment  stimulating  animal  growth,  produced  the  Blue  limestone.    Here 


88  DLXOX    QUADRANGLE 

in  a  gigantic  funeral  mound  are  heaped  the  remains  of  the  myriad  animals 
that  thronged  the  Platteville  ocean.  Clear  water  alternated  with  muddy, 
for  layers  of  shell  limestone  or  compacted  coquina  an  inch  or  two  thick 
are  separated  by  irregular,  shaly  laminae  which  are  rarely  half  an  inch 
in  thickness.  These  interlayered  materials  do  not  form  distinct,  parallel 
beds,  since  they  have  warped  and  wrinkled  greatly  during  compacting. 
On  cliff  exposures,  weathering  has  etched  away  the  shaly  laminations,  leav- 
ing small  bodies  of  purer  limestone  in  relief  on  a  lumpy  surface  of  thin, 
irregular,  lenticular  beds. 

The  list  of  Platteville  fossils  indicates  the  variety  of  the  animal  life. 
Their  number  is  proportionate  to  their  variety.  Every  cubic  inch  of  the 
fossiliferous  Blue  limestone  contains  fragments  of  one  or  more  an'mal 
structures.  They  were  buried  in  the  mud  of  a  quiet  ocean,  unmarred  by 
rolling.  Dolomitization  has  not  affected  them  and  they  preserve  their 
original  features  perfectly.  From  the  10-foot  long  orthoceras  to  the  deli- 
cate, lacy  bryozoa.  they  preserve  the  best  record  of  the  contemporary  life 
that  any  formation  in  this  area  affords. 

Sponges  were  abundant  at  times,  and  the  fine  collection  of  Dr.  Everett4 
was  made  in  this  area.  A  duplicate  of  much  of  this  collection  is  pre- 
served in  the  Dixon  Public  Library.  Brachiopods  and  gastropods  are  the 
most  abundant  forms,  but  representatives  of  all  phyla  except  vertebrates 
and  protozoa  are  found.  Accumulation  of  all  these  forms  with  very  thin 
interlaminated  clays  produced  a  mass  of  fossils  which  is  now  about  45  feet 
thick,  but  probably  was  more  than  twice  as  thick  before  compacting  and  con- 
solidating. 

The  character  of  the  deposits  changed  sharply;  and  slightly  fossilifer- 
ous, very  fine-grained,  calcareous  muds  were  deposited  to  form  the  Glass 
Rock.  Fossils  are  comparatively  rare  in  this  rock.  Animals  or  plants,  or 
both,  must  have  been  present,  however,  in  great  quantity  as  this  material 
accumulated,  for  fresh  rock,  when  freshly  broken,  has  a  strong  odor  of 
petroleum.  This  distinctive  odor  was  noted  in  only  one  other  rock  in  the 
area — a  dense  limestone  bed  in  the  Lowell  Park. 

Irregular,  often  branching,  masses  of  dolomite  penetrate  the  Glass  Rock 
at  all  horizons.  These  masses  have  the  size  and  shape  of  fillings  of  very 
large  worm-borings,  or  the  cavities  left  by  decaying  plants  that  were  buried 
upright  in  the  lime  mud.  They  never  contain  fossils.  Whatever  their 
origin,  these  masses  mark  the  beginning  of  the  return  of  magnesian  sedi- 
ments. 

Either  the  ocean  floor  rose  above  the  surface,  or,  less  probably,  it 
rose  high  enough  so  that  waves  rubbed  and  scraped  away  the  top  of  the 


4  Ulrich,    E.    O.,    and    Everett,    Oliver,    Descriptions    of    Lower    Silurian     sponj 
Geol.   Survey  of  Illinois,   vol.   8,   pp.    253-2S2,   1890. 


GEOLOGIC    HISTORY  89 

Glass  Rock.  A  slight  erosional  unconformity  appears  at  some  places  be- 
tween this  and  the  overlying  Lowell  Park  member.  Residual  soil  and  worn, 
rolled  chert  and  limestone  pebbles  are  not  found  in  this  area,  but  mark 
the  erosion  line  in  a  quarry  in  the  north  part  of  Ashton,  three  miles  e:ist 
of  the  Dixon  quadrangle.  This  unconformity  has  not  been  reported  in 
surrounding  areas,  and  it  may  be  a  local  feature  marking  a  temporary  ex- 
posure when  elevation  along  the  La  Salle  anticline  was  more  rapid  than  the 
gradual  subsiding  of  the  ocean  floor  over  the  whole  Mississippi  Valley. 
It  does  not  indicate  any  important  break  in  the  sedimentation  of  this  region. 

The  Lowell  Park  member  of  the  Platteville,  formed  in  Decorah  time, 
marks  the  transition  from  true  limestone  to  the  pure  dolomite  of  the 
Galena.  It  is  more  argillaceous  than  either  the  underlying  or  overlying 
formations,  and  thereby  indicates  the  muddy  ocean  in  which  it  was  formed. 
Streams  poured  great  quantities  of  mud  into  the  ocean  to  the  northwest 
of  this  region,  forming  the  thick  Green  Shales  of  Minnesota  and  the  some- 
what thinner  Decorah  shale  of  northwestern  Iowa;  and  the  clay  which 
was  carried  farthest  from  shore  in  the  Dixon  area  mingled  with  the  lime 
muds  to  make  the  argillaceous  Lowell  Park.  At  first  the  sediment  was 
highly  magnesian,  being  almost  a  dolomite  and  containing  a  moderate 
percentage  of  clay.  The  clay  content  of  the  ocean  varied  greatly  during 
Decorah  time,  but  increased,  on  the  whole,  to  the  end  of  the  Platteville. 
Magnesian  deposition  varied  inversely,  the  more  argillaceous  beds  being 
less  magnesian. 

Life  in  the  ocean  was  less  flourishing,  or  at  least  its  remains  are  less 
numerous.  A  few  new  animals  developed,  notable  among  which  is  the 
coral,  Columnaria  halli,  a  typical  fossil  of  Decorah  time.  Plants  are  repre- 
sented, for  the  first  time  since  the  Shakopee,  by  abundant  fucoids  in  the 
more  shaly  layers. 

Dolomitization  was  completed  in  each  bed  before  the  next  bed  was 
deposited,  for  dolomite  and  limestone  are  here  interbedded.  and  in  general 
the  lower  strata  of  the  Lowell  Park  are  much  more  dolomitic  than  the 
upper  ones,  indicating  that  the  magnesia  could  not  have  been  introduced 
later  by  waters  descending  from  the  Galena. 

GALENA    STAGE 

Without  interruption,  so  far  as  is  known,  the  clear  waters  of  Galena 
time  succeeded  the  muddy  Decorah-Lowell  Park  ocean.  Abundant  plant 
material  constitutes  the  oil  rock  at  the  base  of  the  Galena  in  northwestern 
Illinois,  but  no  trace  of  plant  life,  either  as  casts  or  in  oil  rock,  appears 
in  this  quadrangle.  In  the  beginning  of  the  Galena  stage,  a  clear  ocean 
apparently  inhabited  chiefly  by  gastropods,  corals,  and  sponges,  deposited 
a   lime   mud   which   has    recrystallized    to    form    the    characteristic    coarse- 


90  DIXON    QUADRANGLE 

grained,    porous    dolomite.      This    type    of    sedimentation    went    on   to    the 
close  of  the  sedimentary  record  in  this  quadrangle. 

The  high  porosity  of  the  Galena  suggests  that  it  was  altered  to  dolo- 
mite after  consolidation.  No  other  evidence  for  this  suggestion  is  known 
in  this  region.  Calvin  and  Bain5  have  presented  evidence  that  the  Galena 
in  Iowa  has  been  dolomitized  since  deposition  and  that  the  depth  of  dolo- 
mitization  varied  greatly  at  different  localities.  At  times,  sponges  were 
especially  abundant,  covering  the  entire  ocean  floor  and  producing  two  dis- 
tinct horizons  which  can  be  used  as  markers  for  determining  distance 
from  the  base  of  the  formation.  Again,  the  amount  of  silica  deposited 
increased  greatly  and  in  the  resulting  chert  the  only  Galena  bryozoa  of  the 
quadrangle  are  preserved.  Presumably,  the  silica  was  extracted  from  the 
water  by  animals  or  plants,  for  there  is  no  sand  or  appreciable  increase  of 
other  clastic  sediment  at  this  horizon. 

LATER  PALEOZOIC   RECORD 

Surrounding  areas  show  that  following  the  Galena  stage,  the  ocean 
withdrew.  When  it  returned,  it  was  more  muddy  and  the  Maquoketa  series 
of  calcareous  shales  and  limestones  covered  the  area.  In  a  clearer  water, 
the  Niagaran  limestone  formed  above  the  Maquoketa. 

During  the  Devonian  period,  the  relations  of  continent  and  ocean  were 
entirely  reversed,  and  the  open  sea  lay  to  the  northwest  and  land  to  the 
southeast.  Black  shales  and  near-shore  deposits  mark  this  period  in  Ohio, 
Indiana  and  southern  Illinois.  Limestone  formed  in  clearer  water  at  Rock 
Island,  and  in  North  Dakota  and  Manitoba.  Probably,  Devonian  sediments 
once  covered  this  area,  but  they  have  been  entirely  removed. 

There  is  no  evidence  of  the  presence  of  later  Paleozoic  formations  in 
this  area,  although  it  is  entirely  possible  that  the  coal  fields  originally  ex- 
tended at  least  this  far  north. 

Cenozoic  Era 
TERTIARY  PENEPLANATION 

Aside  from  some  thoroughly  weathered  gravels  of  probable  Tertiary 
age,  no  sediments  exist  in  this  or  neighboring  areas  to  indicate  the  history 
of  events  from  the  Pennsylvanian  to  the  Pleistocene.  During  this  time  all 
post-Galena  sediments  were  removed  from  this  area,  and  in  the  late  Tertiary 
a  broad  peneplain  developed  over  northern  Illinois  and  southern  Wisconsin. 
In  the  Cretaceous-Tertiary  interval,  several  partial  peneplains  were  cut  in 
the  Appalachian  mountains.     Similar  surfaces  may  have  been  formed  here; 

5  Calvin,   Samuel,   and   Bain,   H.   F.,   Geology   of  Dubuque    County:    Iowa   Geol.    Sur- 
vey,   vol.    10,   pi..    407-412,    1900. 


GEOLOGIC    HISTORY  91 

but,  if  so,  they  were  entirely  removed  in  the  development  of  the  existing 
peneplain. 

Renewed  erosion  in  the  late  Tertiary  or  early  Pleistocene  dissected  the 
peneplain  considerably  before  Illinoian  glaciation.  Since  that  interruption, 
further  stream  work  has  cut  deep  valleys,  and  along  Rock  and  Kyte  rivers 
the  peneplain  is  entirely  destroyed.  If  the  glacial  deposits  could  be  stripped 
away  and  the  valleys  filled  to  the  level  of  the  rock  in  the  intervening  uplands, 
the  peneplain  would,  be  restored  as  a  gently  rolling  plain  rising  from  about 
760  feet  above  sea  level  at  the  south  to  an  elevation  of  900  feet  in  the  north. 

The  following  cross  sections  illustrate  this  surface.  In  a  strip  four 
miles  wide  across  the  southern  end  of  the  quadrangle,  the  highest  rock  points 
either  outcropping  or  encountered  in  wells  are  an  outcrop  of  Galena  dolo- 
mite in  sec.  28,  South  Dixon  Township  at  750  feet ;  a  quarry  in  the  Galena 
in  sec.  19,  Nachusa  Township  with  a  top  elevation  of  780  feet;  limestone, 
which  is  probably  Platteville,  in  a  well  in  sec.  28,  Nachusa  Township  at 
780  feet ;  St.  Peter  sandstone  in  a  well  in  sec.  29,  Bradford  Township  at 
778  feet,  and  a  Platteville  outcrop  in  sec.  32,  Bradford  Township  at  785 
feet.  The  rock  surface  shows  a  uniform  elevation  at  its  higher  points  of 
about  780  feet,  while  the  thickness  of  the  exposed  beds  is  over  250  feet.  A 
similar  section  two  miles  north  of  Dixon  would  show  the  Galena  dolomite 
at  789  feet  on  Pennsylvania  Avenue  and  at  780  feet  in  Rock  River  bluffs ; 
the  vSt.  Peter  at  800  feet  two  miles  east  of  the  river  and  at  790  feet  a  mile 
east  of  Franklin  Creek ;  and  in  the  next  two  miles,  the  Shakopee,  St.  Peter 
and  Blue  member  of  the  Platteville  all  outcrop  between  elevations  of  790 
and  820  feet.  Along  this  section  the  peneplain  elevation  is  about  800  feet. 
Another  east-west  section  a  mile  north  of  Pennsylvania  Corners  would  show 
the  Galena  dolomite  in  a  well  at  the  southeast  corner  of  sec.  19,  Pine  Creek 
Township,  at  840  feet ;  a  mile  and  a  half  east,  the  Galena  outcrops  on  the 
south  side  of  sec.  21  at  8-10  feet ;  east  of  Oak  Ridge  Road  the  Blue  member 
of  the  Platteville  outcrops  at  860  feet  on  the  south  side  of  sec.  24;  the  wSt. 
Peter  makes  a  remnant  of  the  upland  in  sec.  22,  Nashua  Township  at  about 
850  feet.  In  this  section  the  peneplain  surface  is  fairly  well  outlined  at  850 
feet  above  sea  level. 

Martin0  has  argued  that  the  land  forms  of  southern  Wisconsin  and 
northern  Illinois  are  not  peneplain  remnants,  but  rather  are  the  normal  de- 
velopments of  erosion  on  a  series  of  gently  dipping  hard  and  soft  forma- 
tions. His  position  may  be  summarized  briefly  as  follows  :  The  entire  dis- 
trict consists  of  six  formations  gently  dipping  southward.  Erosion  remove 
the  Potsdam  (St.  Croix),  St.  Peter  and  Richmond  (Maquoketa)  strata 
more    readily    than    the    Lower    Magnesian    (Prairie    du    Chien),    Trenton 


6  Martin,    Lawrence,    Physiography    of   Wisconsin:    Wisconsin    Geol.    and    Nat.    Hist. 
Survey   Bull.    36,    pp.    63-70,    1916. 


92 


DIXOX    QUADRANGLE 


(Platteville) -Galena,  and  Niagaran,  leaving  these  formations  outcropping 
in  cuestas  or  unsymmetrical  hills,  each  consisting  of  a  nearly  horizontal  re- 
sistant formation  underlain  by  a  softer  rock.  Erosion  of  the  non-resistant 
formation  undermines  the  harder  one.  and  makes  one  side  of  the  hill  a  bluff, 
or  steep  slope,  while  the  other  slope  approximates  the  dip  slope  of  the  upper 
formation  (fig.  12,  line  A-B).  These  limestone  formations  are  supposed 
to  make  three  north- facing  cuestas  with  a  lowland,  or  valley  lying  on  the 
northern  side  of  each,  where  the  sandstones  and  shales  outcrop. 

Martin's  cross  sections7  show  that  the  tops  of  all  the  hills  closely  ap- 
proach a  line,  which  in  three  dimensions  would  he  a  peneplain,  rather  than 
a  series  of  steps  such  as  characterize  a  repeated  cuesta  topography.  The 
limestones  capping  the  cuestas  form  wedge-shaped  masses,  due  to  the  bevel- 
ing of  this  peneplain  instead  of  maintaining  their  normal  thickness  nearly 
to  the  cuesta  face  and  then  thinning  rapidly  toward  the  bluff.  In  time  the 
normal  cuesta  features  of  a  belted  coastal  topography  will  develop  and 
eliminate  all  trace  of  the  Tertiary  peneplain.     The  present  upland  of  the 


Fig.  12.  Diagram  showing  cuestas,  AB,  resulting  from  erosion  of 
gently  inclined  rocks  of  varying  resistance;  a  peneplain  CD 
later  beveling  these  formations;  cuestas,  EFGHK.  developed 
by  dissection  of  the  peneplain;  and  cuestas,  EMGNK,  result- 
ing from  complete  removal  of  the  peneplain.  The  Dixon  area 
had  reached  stage  EFGHK  before  glaciation. 


region  is  interpreted  as  a  peneplain  because,  (1)  the  hills  approach  a  single 
plane  surface  which  occurs  on  all  formations,  (2)  the  limestones  are  bev- 
eled by  this  surface  into  wedge-shaped  masses.  (3)  conversely,  the  back 
slopes  of  the  cuestas  do  not  approach  parallelism  with  the  dip  of  the  strata, 
and  (4)  in  the  limited  area  of  the  Dixon  quadrangle  where  there  is  less 
opportunity  for  error  owing  to  long-distance  projections,  a  plane  surface  ap- 
pears on  both  the  cuesta-forming  limestones  and  the  less  resistant  sandstone. 
The  age  of  the  peneplain  is  commonly  stated  as  Tertiary.  There  are 
no  sediments  in  the  region  by  which  it  can  he  precisely  dated.  Its  age  is 
determined  in  part  by  correlation  with  gravels  in  southern  Illinois  and  in 
part  by  correlation  with  more  distant  topographic  features. 


Op.   cit.,   figs.   12,   14. 


GEOLOGIC    HISTORY 


93 


Following  the  development  of  the  peneplain,  the  region  was  uplifted 
relatively,  and  the  rejuvenated  streams  dissected  the  old  surface  to  a  con- 
siderable extent  before  Illinoian  glaciation.  In  areas  of  St.  Peter  outcrop 
the  peneplain  was  largely  destroyed  and  steep-sided  valleys  were  developed, 
while  in  the  limestone  areas,  wider  and  shallower  valleys  were  eroded.  The 
resulting  topography  was  buried  by  the  Illinoian  till,  and  in  most  places  can 
be  reconstructed  only  from  well  logs  and  a  few  exposures  where  post-Illi- 
noian  valleys  intersect  the  preglacial  valley  systems.  The  Rock  River 
valley  has  been  greatly  enlarged  since  the  glacial  invasion,  as  shown  by  the 
absence  of  glacial  deposits  from  most  of  its  walls  and  the  rapid  erosion  it 
is  now  experiencing.  In  its  present  form,  the  valley  presents  a  topography 
similar  in  most  respects  to  that  sculptured  in  the  peneplain  before  glaciation 
(fig.  13).  The  comparison  is  not  entirely  accurate,  for  Rock  Valley  is 
largely  underlain  by  one  formation,  the  St.  Peter,  and  accordingly  it  pre- 


Fig.  13.  Rock  River  valley  and  the  Tertiary  peneplain. 
Looking  northeast  along  Rock  River  from  Castle  Rock,  SE.  % 
NE.  14  sec.  19,  T.  23  N.,  R.  10  E.  Cultivated  terraces  of  the  valley 
train  on  either  side  of  the  river,  timbered  slopes  of  St.  Peter  sand- 
stone along  the  bluffs,  and  remnants  of  the  Tertiary  peneplain  on  the 
sky  line.  At  the  left,  the  peneplain  bevels  the  Glass  Rock  member  of 
the  Platteville;  in  the  center,  the  Buff  member  outcrops  on  the 
Devils  Backbone  and  at  the  right,  St.  Peter  sandstone  and  Buff  lime- 
stone support  the  peneplain.  In  the  distance,  the  peneplain  may  be 
seen  north  of  the  Oregon  basin,  where  it  cuts  the  Platteville  and 
Galena  formations. 

sents  few  examples  of  the  limestone-bluff  topography  that  pre-Illinoian  ero- 
sion produced  in  many  areas.  In  the  Driftless  Area  in  the  northwestern 
corner  of  the  State,  the  present  surface  resembles  more  closely  the  Dixon 
landscape  of  early  Pleistocene  time. 


94 


DIXON    QUADRANGLE 


PLEISTOCENE  PERIOD 


At  the  close  of  Tertiary  time,  climatic  changes  caused  the  development 
of  the  continental  glaciers  which  characterized  the  Pleistocene  (fig.  14). 
Of  the  five  glacial  invasions  of  the  United  States,  at  least  two  and  pos- 
sibly three  entered  the  Dixon  quadrangle. 


Fig.  14.  Map  of  area  covered  by  the  North  American  ice- 
sheets  of  the  glacial  epoch  at  their  maximum  extensions, 
showing  the  approximate  southern  limit  of  glaciation, 
the  three  main  centers  of  ice  accumulation,  and  the 
driftless  area  within  the  border  of  the  glaciated  region. 
(U.  S.  Geol.  Survey.) 


PRE-ILLINOIAN    TIME 

Weathered  glacial  boulders  in  the  Illinoian  till  clearly  represent  an 
earlier  glaciation  and  must  have  been  incorporated  in  the  Illinoian  till  while 
frozen.     There  is  no  positive  evidence  that  the  boulders  were  in  the  Dixon 


GEOLOGIC    HISTORY  95 

area  when  they  were  picked  up  by  the  Illinoian  ice,  and  it  is  possible  they 
were  transported  a  long  distance  from  the  site  of  their  earlier  deposition 
and  thorough  weathering.  Cady8  described  some  till  that  is  quite  definitely 
older  than  Illinoian  about  25  miles  south  of  this  quadrangle.  Leverett9  and 
Alden10  discussed  evidences  of  pre-Illinoian  glaciation  in  neighboring  areas, 
but  had  less  definite  evidence  than  Cady,  and  arrived  at  the  conclusion  which 
applies  to  the  Dixon  area,  namely,  that  while  there  is  much  evidence  suggest- 
ing a  pre-Illinoian  glaciation  of  this  area,  it  is  not  proved.  Certainly  only 
the  Illinoian  and  later  invasions  have  appreciably  affected  the  present  topog- 
raphy and  soils. 

ILLINOIAN   GLACIATION 

The  Illinoian  ice-sheet  advanced  into  this  area  from  the  southeast, 
overriding  and  displacing  the  drainage  systems  and  burying  the  southern 
part  of  the  quadrangle  at  some  places  more  than  180  feet  deep  in  till. 

Evidence  of  the  movement  from  the  southeast  is  found  in  glacial  stria- 
tions  which  have  been  uncovered  in  the  stripping  of  till  from  the  Sandusky 
Cement  Company's  quarry  northeast  of  Dixon.  Seven  sets  of  grooves 
or  striations  were  found  on  the  surface  of  the  Platteville  glass  rock.  Their 
direction  varied  from  N.  75°  W.  to  N.  84°  W.,  averaging  N.  80°  W. 
"Stoss  and  lee"  phenomena  developed  on  a  small  scale  by  harder  fossils 
show  clearly  that  the  movement  was  westerly,  and  not  easterly.  Further 
evidence  of  the  northwesterly  movement  of  the  ice  is  given  by  the  occur- 
rence of  coal  in  the  till,  and  the  northwesterly  dip  of  all  cross-beds  in  the 
Grand  Detour  esker. 

The  amount  of  erosion  by  the  ice-sheet  cannot  be  approximated 
because  of  lack  of  knowledge  of  the  preglacial  surface.  Filling  of  valleys 
can  be  approximated  if  sufficient  records  of  deep  wells  are  available.  It 
has  been  shown  that  the  glacial  till  averaged  more  than  60  feet  in  that  portion 
of  the  till  plain  which  is  still  undissected. 

By  filling  valleys  and  eroding  uplands,  glaciation  greatly  reduced  the 
relief  and  ruggedness  of  most  parts  of  the  area.  Outcrops  and  wells  in 
the  southern  part  of  the  area  indicate  a  marked  smoothing  of  the  surface  by 
till  deposition.  The  extreme  case  is  presented  by  sec.  28,  South  Dixon 
Township,  where  a  relief  of  at  least  187  feet  and  an  original  slope  of  at 
least  250  feet  per  mile  are  shown  by  the  buried  rock  surface.  In  no  case 
where  the  original  till  plain  is  preserved,  does  it  slope  over  TO  feet  per  mile, 
although  this  slope  probably  was  exceeded  in  some  of  the  partially  filled 

8  Cady,  G.  H.,  Geology  and  mineral  resources  of  the  Hennepin  and  LaSalle 
quadrangles:   Illinois   State   Geol.   Survey  Bull.    37,   pp.    70-72,    1919. 

9  Leverett,  Frank,  The  Illinois  glacial  lobe:  U.  S.  Geol.  Survey  Jlmi,  38,  pp.  L05-118, 
1899. 

10  Alden,  W.  C,  The  Quaternary  geology  of  southeastern  Wisconsin:  U.  S.  Geol. 
Survey  Prof.  Paper  106,  p.   153,   1918. 


96  DIXON    QUADRANGLE 

valleys  which  have  since  been  re-excavated.  A  good  example  of  the  change 
in  topography  produced  by  glaciation  is  the  contrast  between  the  parts  of 
Franklin  Creek  valley  north  and  south  of  the  Chicago  and  Northwestern 
Railway.  The  headwaters  of  the  stream  flow  through  a  slightly  dissected, 
gently  rolling  till  plain.  In  the  middle  reaches  of  the  valley.  post-Illinoian 
erosion  of  the  sandstones  and  limestones  has  developed  below  the  till  plain 
a  rugged,  ravine  topography,  which  is  probably  similar  to  the  sharper  val- 
leys of  the  early   Pleistocene  surface. 

The  climate  changed:  melting  of  the  ice  exceeded  its  late  of  accumu- 
lation ;  the  glacier  dwindled,  and  its  margin  retreated.  In  the  final  stages 
of  the  glacier,  the  Grand  Detour  esker  was  formed. 

SANGAMON    INTERGLACIAL    EPOCH 

When  the  ice  disappeared,  fresh  blue-gray  till  was  exposed  to  the 
attack  of  various  weathering  processes.  Carbonates  were  dissolved  from 
the  upper  four  to  six  feet  of  the  till,  while  oxidation  reddened  its  surface 
and  changed  its  color  to  bull  for  an  average  depth  of  10  feet.  In  extreme 
cases,  where  the  ground-water  table  was  low.  oxidation  extended  as  much 
as  "2-3  feet  into  the  till.  Black  soil  is  commonly  present  beneath  the  loess, 
showing  that  vegetation  mantled  the  surface  during  this  stage.  A  light- 
gray,  sticky,  thoroughly  leached  material,  called  gumbotil,  resulted  from 
the  Sangamon  weathering,  and  later  was  buried  in  many  places  by  the  lcess. 
In  this  quadrangle,  it  was  found  beneath  ,8  inches  of  loess,  which  was 
calcareous  at  the  base,  in  sec.  14.  T.  21  X..  R.  10  E.  Leighton  has  also 
found  gumbotil  at  various  points  outside  the  Dixon  area  on  the  weathered 
surface  of  the  Illinoian  till. 

Many  of  the  original  depressions  on  the  till  surface  were  drained, 
and   a    stream   pattern   established   which   is    essentially   that   of   today. 

IOWAX     GLACIAL     EPOCH 

While  evidence  is  not  conclusive,  it  appears  that  during  the  Iowan 
stage,  the  ice  invaded  the  Dixon  area  as  a  part  of  the  lobe  which  pushed 
into  the  Green  River  basin  from  the  east.  In  the  opinion  of  Leighton.  the 
Iowan  sheet  did  not  remain  within  the  quadrangle  long,  for  the  terminal 
ridge  which  lies  across  the  southern  part  of  the  area  is  only  moderately 
developed  and  there  are  some  spots  northeast  of  Amboy  where  gumbotil 
is   exposed,   in   striking   contrast   to   the   relatively    fresh   drift   elsewhere. 

PEORIAN     IXTERGLACIAL     EPOCH 

Just  as  the  larger  part  of  the  Inc.--  in  northern  Illinois  and  eastern 
Iowa  appears  to  lie  of  late  Iowan  and  early  Peorian  age.  so  does  deposi- 
tion of  the  loess  in  the  Dixon  quadrangle  appear  to  have  begun  soon  after 
the  margin  of  the  Iowan  ice-sheet  commenced  its  retreat  and  to  have  con- 


GEOLOGIC    HISTORY  97 

tinued  into  Peorian  time.  Wherever  the  base  of  the  loess  overlying  Iowan 
till  is  calcareous,  the  drift  is  fresh,  unleached,  and  blue-gray,  showing  no 
signs  of  erosion  or  exposure.  For  a  time,  the  rate  of  loess  accumulation 
was  comparatively  rapid,  and  exceeded  the  rate  of  leaching,  but  eventually 
the  relation  was  reversed,  and  leaching  and  oxidation  began  to  produce 
the  present  weathered  zone.  Where  the  loess  is  more  than  five  feet  thick,  its 
base  is  commonly  calcareous,  but  above  that,  the  calcium  carbonate  has  been 
dissolved  away.  Erosion  has  removed  much  of  the  loess  from  the  valley 
slopes  and  probably  all  of  it  from  the  valley  bottoms.  Loess  formation 
is  continuing  at  a  slow  rate  today,  but  most  of  the  silt  is  oxidized  and 
leached,  and  the  new  loess  is  indistinguishable  from  the  surface  loam. 

WISCONSIN    EPOCH 

The  Peorian  interglacial  stage  was  brought  to  a  close  by  the  Wisconsin 
glacier  which  approached  the  area,  but  did  not  reach  it.  The  Lake  Michi- 
gan lobe  of  the  glacier  followed  the  depression  now  occupied  by  Lake 
Michigan  and  spread  south  and  southeast  into  Illinois,  covering  the  area 
outlined  by  the  Bloomington  moraine,  which  runs  about  10  miles  east  and 
18  miles  south  of  the  area.  In  late  Wisconsin  time,  the  glacier  re-invaded 
the  border  area  of  Lake  Michigan  and  developed  the  Green  Bay  lobe,  which 
pushed  down  Green  Bay  and  across  the  low  divide  into  Rock  River  basin, 
finally  stopping  near  Janesville,  Wisconsin,  about  75  miles  (measured  along 
the  river)  north  of  the  Dixon  quadrangle.  When  it  entered  Green  Bay, 
it  dammed  Fox  River  and  formed  a  lake  which  found  an  outlet  south- 
west to  Rock  River.  This  new  supply  of  clear  lake  water  enabled  the 
Rock  to  erode  vigorously  and  remove  much  of  the  valley  train  that  had 
filled  Kyte  River  in  Early  Wisconsin  time  and  extended  down  the  channel 
of  tbe  Rock.  As  the  glacier  advanced,  the  lake  grew  smaller,  until  the 
ice  overtopped  the  divide  and  water  from  the  melting  ice  swept  great 
quantities  of  sand  and  gravel  into  Rock  River.  The  supply  of  material 
was  too  great  for  the  stream  to  move  and  it  deposited  the  surplus  sand 
and  gravel,  forming  the  Late  Wisconsin  valley  train.  By  continued  depo- 
sition, Rock  River  built  up  its  channel  to  keep  pace  with  Mississippi  River 
which  was  being  filled  with  outwash  from  the  Superior  lobe. 

Deep  filling  at  Janesville  increased  the  gradient  and  consequently  the 
velocity  of  Rock  River,  until  equilibrium  was  established  between  the  sup- 
ply and  removal  of  outwash.  The  Wisconsin  glacier  melted  away,  and 
since  that  time  Rock  River  has  been  removing  the  overload  that  it  dropped 
to  form  the  valley  train.  When  the  glacier  retreated,  Rock  River  was 
flowing  through  Dixon  about  45  feet  above  its  present  level,  and  its  total 
filling  amounted  to  more  than  105  feet.  Tributary  streams  that  carried 
much  sediment  built  up  to  the  level  of  Rock  River,  while  others  were  ponded 


95  DIXOX    QUADRANGLE 

and  much  line  sand  was  swept  into  these  temporary  lakes  from  the  main 
river. 

POST-ILLINOIAN    DRAINAGE    DEVELOPMENT 

When  the  Illinoian  ice-sheet  melted  away,  it  left  this  quadrangle  nearly 
completely  buried  under  an  irregular,  thick  blanket  of  till  and  other  drift. 
Many  valleys,  especially  the  smaller  ones,  were  completely  obliterated ;  oth- 
ers were  partially  rilled  or  dammed  with  drift.  Surface  water  collected 
in  shallow  depressions  to  form  ponds  and  small  lakes,  or  drained  away 
along  irregular,  crooked  courses.  The  new  channels  were  independent  in 
man}"  places  of  the  preglacial  drainage,  and  in  some  instances  utilized  parts 
of  two  or  more  old  valleys.  Rains  and  melting  ice  and  snow  provided 
water  which  scoured  out  new  channels.  In  no  case  is  the  present  drainage 
materially  different  from  that  which  developed  on  the  withdrawal  of  the 
Illinoian  ice.  but  marked  departures  from  the  pre-Illinoian  system  are 
known. 

In  studying  the  drainage  changes,  trustworthy  comparisons  and  con- 
clusions as  to  ages  of  valleys  usually  can  be  made  only  between  channels 
in  similar  rock.  Rapid  erosion  of  the  sandstone  has  developed  many 
broad  valleys  since  glaciation.  while  comparatively  little  erosion  of  lime- 
stone has  occurred.  Pine  Creek  illustrates  the  combination  of  old  and  new 
drainage.  In  sees.  T.  5.  10.  11.  and  IT.  T.  "23  X..  R.  9  E..  small  tributaries 
occupy  broad,  gentle-sloped,  preglacial  valleys,  now  partly  rilled  with  till, 
while  the  main  stream  flows  through  a  narrower,  steeper-sided  valley  in 
sees.  9.  16.  22.  and  27,  which  has  been  excavated  since  the  Illinoian  invasion, 
in  the  same  limestone  as  the  preglacial  valleys.  A  depression  in  the 
surface  and  an  absence  of  rock  outcrops  indicate  that  the  old  valley  in  the 
northern  part  of  sec.  9  formerly  continued  southeastward  through  sec.  10  to 
the  broad  valley  in  sec.  15.  The  connection  of  valleys  in  sees.  T.  S.  and 
IT  is  not  clearly  established,  but  absence  of  outcrops  and  occurrence  of  till 
in  valley  walls  suggest  a  drainage  line  through  sec.  "21  to  the  main  channel 
in  northeastern  sec.  £8  and  across  the  present  divide  into  the  southeastern 
part  of  the  same  section.  The  changes  in  this  drainage  system  appear  to 
have  resulted  from  damming  and  filling  of  the  valleys  by  till. 

A  comparatively  broad  sandstone  valley  in  sec.  22  and  a  similar  one 
in  sec.  -4  of  the  township  to  the  south  (T.  22  X..  R.  9  E.)  are  not  occupied, 
while  the  stream  uses  adjacent,  narrower,  younger  valleys  excavated  in  the 
same  formation.  The  abandoning  of  these  old  valleys  is  not  necessarily 
due  to  damming  bv  till,  for  it  may  have  resulted  from  the  rilling  connected 
with  the  Wisconsin  valley  trains  raising  the  stream  until  it  flowed  over 
narrow,  low  divides  between  tributaries  of  the  main  stream.  If  the 
stream  still  occupied  this  position  when  it  resumed  its  downward  erosion 
after   the   filling,   the   new    courses   could    then   have   been    established. 


T 


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along  irr 
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after  t! 


GEOLOGIC    HISTORY  99 

The  most  important  drainage  change  in  this  region  is  that  of  Rock 
River.  Plate  IV  is  modified  from  Leverett11  and  the  following  account 
of  changes  in  river  course  is  a  review  of  his  work  outside  the  Dixon  quad- 
rangle. Within  this  area,  the  writer  agrees  with  the  earlier  interpretation 
except  as  to  Chamberlain  and  Pine  creeks. 

From  a  careful  study  of  the  present  drainage  system,  of  the  distri- 
bution of  abandoned  and  till-nlled  valleys,  and  numerous  deep  well  rec- 
ords, it  is  known  that  before  Illinoian  glaciation,  Rock  River  followed 
a  course  similar  to  the  present  one  south  as  far  as  Rockf ord ;  but  the  old 
valley  leaves  the  present  stream  a  short  distance  south  of  that  city  and 
continues  on  a  southerly  course  to  the  present  Illinois  valley  near  Henne- 
pin. Leverett  believes  that  preglacial  Mississippi  River  turned  east  near 
Clinton,  Iowa,  joined  Rock  River  northwest  of  Princeton  and  the  com- 
bined stream  flowed  down  the  present  Illinois  valley  to  the  present  Mis- 
sissippi River,  near  Alton.  Kyte  River  flowed  east  to  join  Rock  River 
southwest  of  Rochelle.  Pine  Creek  entered  the  Dixon  quadrangle  north 
of  The  Pines,  but  turned  southeast  from  sec.  9  into  sec.  10  along  the  route 
of  the  Chicago,  Burlington  and  Quincy  Railroad,  south  past  Columbian 
School  and  then  followed  nearly  the  present  course  to  Rock  River.  Aban- 
doned valleys  in  sec.  22,  T.  23  N.,  R.  9  E.,  and  sec.  4,  T.  22  N.,  R.  9  E., 
have  been  mentioned.  Sevenmile  Branch  was  a  tributary  of  Pine  Creek 
from  the  west.  Chamberlain  Creek  had  a  course  similar  to  the  present 
one  to  the  Rock  River,  then  flowed  westward  to  a  point  a  mile  southwest 
of  Grand  Detour  (sec.  14,  T.  22  N.,  R.  9  E.)  where  it  turned  southwest 
through  sees.  14,  15,  and  22  to  join  Pine  Creek  near  the  middle  of  sec.  21. 
Preglacial  Clear  Creek  drained  much  of  the  area  that  its  successor  flows 
through  today,  and  probably  joined  Chamberlain  Creek  in  the  vicinity  of 
Grand  Detour.  The  exact  course  of  Clear  Creek  is  not  definitely  known, 
but  the  broadly  open  valleys,  carrying  till  as  low  as  the  present  streams, 
indicate  a  mature  preglacial  valley  southeast  of  Tealls  Corners.  The 
stream  probably  flowed  northwest  into  sec.  9,  roughly  paralleled  the  road 
southwest  to  sec.  8  and  turned  northwest  again  to  the  present  Rock  River 
valley.  A  tributary  from  the  north  may  have  been  excavating  a  valley 
later  occupied  by  Rock  River,  but  the  absence  of  till  far  down  its  slopes 
indicates  that  this  valley  has  been  greatly  enlarged  and  perhaps  largely 
developed  since  Illinoian  glaciation.  From  the  width,  side  slopes  and 
occurrence  of  till  near  the  flood-plain,  it  seems  probable  that  Clear  Creek 
valley  was  more  mature  before  glaciation  than  was  the  valley  now  occupied 
by  Rock  River  north  of  Taylor  Township. 


11  Leverett,   Frank,   The   Illinois  glacial   lobe:  U.   S.   Geol.    Survey   Mon.   38,    PI.   XII, 

pp.    484-492,    1899. 


100  DIXON    QUADRANGLE 

This  statement  differs  from  Leverett's  only  in  that  he  believed  that 
Pine  Creek  flowed  east  along  the  present  course  of  Rock  River  to  Chamber- 
lain Creek,  and  that  the  latter  stream  originally  flowed  southeast  to  Rock 
River  through  the  southeastern  part  of  the  quadrangle.  The  absence 
of  outcrops  immediately  southeast  of  Chamberlain  Creek  accords  with  his 
hypothesis,  but  recent  drilling  of  water  wells  in  Nachusa  and  China  town- 
ships has  shown  the  St.  Peter  sandstone  within  50  feet  of  the  surface 
across  the  postulated  valley.  From  a  point  a  mile  south  of  Nachusa,  east 
to  Franklin  Creek,  the  greatest  distance  between  wells  which  have  rock 
bottom  is  three-quarters  of  a  mile  and  the  lowest  rock  elevation  is  750  feet, 
which  is  the  depth  of  the  sandstone  in  the  NW.  %  sec.  16,  T.  21  N.,  R. 
10  E.  (PI.  IV).  The  top  of  the  sandstone  in  the  valley  dammed  by  the 
esker  at  Grand  Detour  has  an  elevation  of  less  than  680  feet.  Till  crops 
out  for  more  than  a  mile  in  lower  Pine  Creek  valley  at  680  feet,  and  the 
buried  valley  partly  exposed  by  Clear  Creek  in  sec.  4  has  its  channel  below 
present  stream  level,  which  is  720  feet.  These  streams,  therefore,  could 
not  have  flowed  southeast  along  Chamberlain  Creek  valley.  Positive  evi- 
dence of  western,  rather  than  southeastern  drainage  from  Grand  Detour 
is  offered  by  the  esker-dammed  valley.  Rock  surface  at  the  eastern  end 
of  the  valley  is  below  680  feet  but  above  665,  while  the  western  end  of 
the  valley  does  not  contain  rock  outcrops,  but  the  valley  filling  is  less  than 
660  feet  above  sea  level.  The  fact  that  Rock  Valley  narrows  downstream 
does  not  indicate  that  the  constricted  portion  is  newer  than  that  upstream, 
for  all  the  wider  parts  of  the  valley  in  this  quadrangle  occur  where  the 
easily  eroded  St.  Peter  outcrops  and  all  the  narrow  reaches  are  found 
where  limestone  outcrops  in  the  valley  floor.  The  same  relation  of  valley 
width  to  kind  of  rock  is  even  more  strikingly  shown  in  Pine  Creek 
valley.  Still  further  evidence  is  the  fact  that  limestone  is  found  at  the  Illinois 
Central  Railroad  bridge  over  Rock  River  in  Dixon  at  575  feet,  or  175  feet 
lower  than  the  supposed  Pine  Creek  course  southeast  through  Chamber- 
lain valley.  Some  of  the  depth  may  have  been  attained  in  the  periods 
of  erosion  which  followed  the  Illinoian  glaciation  and  preceded  the  last 
Wisconsin  period  of  valley  filling.  The  limestone  channel  at  the  railroad 
bridge  is  twice  as  wide  as  the  narrowest  part  of  the  postglacial  channel 
of  Rock  River  through  the  St.  Peter  sandstone,  sec.  30,  T.  23  N.,  R.  10  E. 
Since  the  sandstone  is  much  more  easily  eroded  than  limestone,  it  seems 
probable  that  the  limestone  valley  is  largely  preglacial. 

When  the  Illinoian  ice-sheet  advanced  from  the  east,  it  filled  preglacial 
Rock  Valley  east  of  this  quadrangle  with  drift  to  a  depth  exceeding  300 
feet  in  some  places  and  forced  the  river  to  seek  another  route  to  the  south. 
The  ponded  water  rose  until  it  flowed  over  the  Leaf  River  divide  into  Kyte 
River,  overtopped  the  divide  to  the  Chamberlain  Creek  tributary,   flowed 


GEOLOGIC    HISTORY  101 

southwest  to  the  esker  dam  with  an  elevation  of  over  720  feet,  crossed  a 
low  divide  to  the  northwest  into  Pine  Creek  and  followed  its  course  south- 
westward  to  join  Mississippi  River,  which  had  been  pushed  westward  by  the 
ice  and  did  not  return  to  its  original  location  when  the  glacier  melted.  Kyte 
River  valley  was  filled  with  glacial  drift  to  the  east,  and  found  its  outlet 
to  the  southwest  with  Rock  River.     It  is  the  only  clearly  reversed  stream 

in  this  quadrangle. 

RECENT   HISTORY 

Since  the  deposition  of  the  Rock  River  valley  train,  the  age-old  proc- 
esses of  weathering  and  erosion  have  been  active.  The  loess  has  been 
oxidized  and  leached;  where  till  was  close  to  the  surface  it  has  been 
similarly  weathered,  as  was  the  Illinoian  till  before  loess  deposition.  Leach- 
ing of  the  valley  train  gravels  since  Late  Wisconsin  time  has  extended 
12  to  18  inches  beneath  the  surface.  The  loess  overlying  the  Iowan  (?) 
till  is  leached  to  an  average  depth  of  3.9  feet,  but  the  figures  are  not  strictly 
comparable,  because  the  porous  gravel  permitted  water  to  pass  through  it 
rapidly  without  accomplishing  as  much  leaching  as  if  it  had  stood  longer 
in  contact  with  the  pebbles.  In  a  few  places,  the  top  of  the  Galena 
dolomite  has  broken  down  to  a  red-brown  sand  of  dolomite  rhombohedra. 
There  is  no  way  to  determine  how  much  of  this  weathering  is  pre-Illinoian. 
The  denser  Platteville  limestone  rarely  shows  thorough  postglacial  weather- 
ing, but  its  surface  is  commonly  shattered  and  hackly  from  frost  attack  and 
solution. 

With  three  exceptions,  original  depressions  on  the  till  plain  have  been 
destroyed  by  natural  processes.  Lakes  and  ponds  occupied  the  deeper 
basins  when  the  ice  first  retreated.  Loess,  accumulated  plant  matter  and 
sediment  brought  in  by  streams  have  filled  some  of  these,  and  erosion 
of  the  outlet  by  flood  waters  has  probably  drained  a  great  many  others. 
Two  original  depressions  nearly  filled  with  decaying  vegetation  remain 
south  of  the  Chicago  and  Northwestern  Railway  in  sees.  10  and  11,  T.  21 
N.,  R.  9  E.  The  largest  swamp  remnant  on  the  upland  is  located  in  sees. 
18  and  19,  T.  22  N.,  R.  11  E. 

Depressions  have  been  formed  since  glaciation  by  the  piling  up  of  sand 
dunes  and  by  solution  of  limestone  by  ground  water.  Sand  dunes  have 
blocked  a  drainage  line  in  sec.  5,  T.  22  N.,  R.  10  E.,  forming  a  small  lake; 
a  quarter  of  a  mile  north  in  sec.  32,  a  sand-dune  dam  has  produced  another 
pond.     These  are  the  only  bodies  of  open  standing  water  in  the  area. 

Ground  water  dissolves  limestone  and  produces  caves  and  under- 
ground channels.  Where  the  roof  of  a  cave  collapses,  the  surface  falls  and 
the  resulting  depression  is  called  a  sink  hole.  Less  spectacular  is  the  for- 
mation of  a  sink  hole  by  slow  surface  subsidence  as  the  rock  immediately 
beneath  the  soil  is  dissolved. 


102 


DIXON    QUADRANGLE 


The  following  table  summarizes  the  data  on  sink  holes  in  this  area: 


Table  5. — Sink  holes  in 

the  Dixon  quadrangle 

Location 

Surface  rock 

Number 

Diameter 

Depth 

Part  of  sec. 

sec. 

T.N. 

R.  E. 

Feet 

Feet 

Galena  dolomite   

2 

60 

8 

NE.    cor 

19 

22 

9 

Galena  dolomite   

3 

30-60 

4-10 

3E.  y4 

26 

21 

9 

Platteville  limestone.. 

25 

10-100 

5-18 

8E.    14 

27 

22 

9 

NE.   % 

34 

22 

9 

Platteville  limestone.. 

2 

20-30 

4-10 

SE.    14 

16 

22 

9 

Platteville  limestone.. 

2 

25 

10 

NE.   % 

35 

23 

10 

St.  Peter  sandstone... 

1 

40 

8 

NE.   % 

25 

23 

9 

Shakopee  dolomite    . . 

2 

20 

5 

SE.    1/4 

30 

23 

11 

The  sink  hole  in  the  St.  Peter  undoubtedly  results  from  solution  of 
the  underlying  Shakopee.  Southwest  of  Britton  School  (sec.  27,  T.  22 
N.,  R.  9  E.)  the  sink  holes  are  elongated  in  a  northeast-southwest  direc- 
tion, parallel  to  the  strike  of  the  best-developed  joint  system  of  the  Platte- 
ville limestone.  Probably  most  of  the  holes  are  connected  underground. 
One  hole  has  a  large  opening  leading  into  a  channel  three  feet  high  which 
was  followed  a  distance  of  350  feet  past  the  entrance  of  a  second  to  a 
third  hole.  The  channel  was  blocked  by  a  rock  fall  a  short  distance  beyond 
the  third  hole.  Quarrying  operations  have  destroyed  Fuller's  Cave,  which 
once  underlay  the  present  site  of  the  Sandusky  Cement  Company's  quarry. 
Local  tradition  reports  that  this  was  once  a  bandits'  rendezvous.  None  of 
the  other  sink  holes  are  known  to  be  connected  with  caves. 

Sand  dunes  have  been  heaped  up  near  Temperance  Hill  School  (sec. 
27,  T.  21  N.,  R.  10  E.)  ;  in  three  places  on  the  valley  train,  namely,  north 
of  Grand  Detour,  southwest  of  Daysville  and  north  of  Prairieside  School 
(sec.  7,  T.  22  N.,  R.  10  E.)  ;  and  also  in  three  places  on  the  Rock  River 
bluffs — a  mile  northwest  of  Grand  Detour,  north  of  Prairieside  School,  and 
in  sees.  20  and  21,  T.  23  N.,  R.  10  E.  All  of  these  dunes  have  formed 
or  moved  since  loess  deposition  was  practically  complete,  for  there  is  no 
loess  superimposed.  The  sands  show  little  rounding;  and  sorting  and  siz- 
ing of  material  are  poor.  Probably  none  of  the  dunes  have  moved  a  mile 
from  the  place  of  origin.  Vegetation  covers  them  completely,  except  where 
overpasturing  has  destroyed  the  plants  and  a  little  sand  has  recently  been 
blown  into  gentle  ripples. 

ASYMMETRICAL    VALLEY    SLOPES,    STREAM    DISPLACEMENT    AND    EXPOSURE    TO 

SUN    AND    WIND 

An  interesting  feature  of  the  drainage  in  this  area  is  a  tendency  of 
the  streams  to  follow  the  south  and  west  sides  of  the  valleys,  and,  by  under- 


GEOLOGIC    HISTORY  103 

cutting,  to  make  those  sides  steeper  than  the  north  and  east  sides.  There 
are  many  exceptions  to  this  statement,  but  where  streams  are  not  affected 
by  rock  outcrops,  they  usually  obey  this  rule.  It  should  be  noted  that  the 
topographic  map  indicates  the  position  of  the  flood-plains  accurately,  but  the 
stream  locations  within  those  plains  are  generalized  and  this  eccentric 
situation  of  the  streams  is  not  so  marked  on  the  map  as  in  the  field.  At 
first,  it  was  believed  that  this  was  an  interesting  case  of  Ferrel's  law  that 
moving  bodies  in  the  northern  hemisphere  tend  to  be  deflected  to  the  right. 
A  south-flowing  stream  would  accordingly  be  thrown  against  its  right,  or 
west  bank,  and  an  east-flowing  stream  against  the  south  side  of  its  valley. 
But  north-flowing  streams  also  follow  the  west  side,  instead  of  the  east 
as  Ferrel's  law  requires,  and  west-flowing  streams  are  more  often  on  the 
south  than  on  the  north  sides  of  their  valleys.  Ferrel's  law  thus  does  not 
explain  the  situation. 

The  north  sides  of  valleys  are  more  exposed  to  the  sun  than  the 
south  sides ;  and  the  afternoon  sun  shines  directly  on  the  east  valley  wall 
when  the  air  is  warmer  than  in  the  morning.  Consequently,  the  east  and 
north  slopes  dry  out  more  quickly  than  the  opposite  sides  of  the  valleys. 
In  Illinois  the  northeast  wind  is  a  cool  rain-bearer,  while  the  southwest 
winds  are  usually  warm  and  drying,  removing  moisture  from  the  north  and 
east  sides  of  valleys.  Thus  the  wind  and  sun  both  tend  to  dessicate  the 
north  and  east  slopes,  which  consequently  have  poorer,  sparser  vegetation. 
With  reduced  plant  protection  and  drier  material,  wind  blows  more  dust 
from  these  slopes ;  run-off  finds  the  soil  more  accessible  for  erosion  and 
meets  less  interference  from  vegetation,  and  creep  is  more  active.  All 
factors  combine  to  erode  the  north  and  east  sides  of  the  valleys  which 
have  gentle  slopes.  The  washed  or  creeping  material  on  reaching  the  flood- 
plain  tends  to  displace  the  streams  to  the  opposite  side  of  the  valley.  There- 
fore, relative  exposure  to  drying  conditions  is  believed  to  be  the  cause  of 
the  stream  locations  on  the  south  and  west  sides  of  their  valleys. 

Demangeon12  has  noted  this  greater  erosion  of  the  east  and  north 
sides  of  valleys  in  Picardy,  France,  and  concluded  that  it  was  due  to  west- 
erly rain-carrying  winds  precipitating  more  water  on  the  east  and  north 
sides  of  the  valleys,  so  that  slopewash  eroded  them  more  rapidly,  built 
up  the  flood-plains  on  them,  and  forced  the  streams  across  to  the  south 
and  west  sides  of  the  valleys. 

In  Illinois,  the  rain-bearing  winds  are  easterly,  yet  the  erosion  is  most 
marked  on  the  east  and  north  sides.  This  fact  suggests  that  the  direction 
of  rain-bearing  winds  is  of  minor  importance.  Differences  of  vegetation 
between  north  and  south  sides  of  valleys  are  well  known  and  abundantly 


12  Demangeon,    Albert,    La  Picardie,   Paris,    p.    77,    1905. 


104  DIXON    QUADKANGLE 

evident  in  this  area.  Erosional  differences  normally  are  closely  related  to 
the  amount  and  luxuriance  of  the  vegetation.  Accordingly,  since  the 
amount  of  drying  exposure  is  correlated  with  the  amount  of  erosion,  and 
the  correlation  with  wind-bearing  rains  is  not  shown  in  this  area,  the 
writer  believes  that  the  position  of  the  streams  and  the  gentle  slopes  of 
the  north  and  east  sides  of  valleys  have  resulted  from  the  exposure  of 
those  sides  to  drying  by  sun  and  wind. 

HUMAN     ACTIVITIES     AND    THEIR     EROSIONAL    EFFECTS 

At  present,  erosion  is  more  rapid  than  it  has  been  at  any  time  since 
vegetation  established  itself  after  the  last  glacial  invasion.  Processes  of 
weathering  and  erosion  are  the  same  as  usual,  but  man  has  greatly  aided 
the  erosional  effects  of  running  water  by  destroying  the  prairie  sod,  clear- 
ing the  timber,  plowing  annually,  quarrying,  draining  the  land  and  min- 
ing. So  great  has  been  the  increase  in  erosion  and  transportation  of  ma- 
terial that  the  Rock  and  all  its  tributaries  are  silt-laden  streams  running 
through  muddy  channels  in  which  carp  thrive,  whereas  when  the  region 
was  first  settled,  Rock  River  had  a  gravel  bottom  which  could  be  seen  at 
depths  of  four  or  five  feet  and  the  mud-loving  carp  was  unknown.  The 
resulting  increase  in  silt  deposition  is  described  in  the  section  on  alluvium. 

Mining  has  had  practically  no  effect  on  this  area,  since  only  one  small 
prospect  has  ever  been  opened  in  it.  Artificial  drainage  is  somewhat  more 
important,  although  its  effects  are  less  notable  here  than  in  swampy  areas 
like  the  Inlet  and  Winnebago  swamps  of  Green  River.  In  the  Dixon 
quadrangle,  little  land  has  been  drained  by  ditches,  so  that  drainage 
has  not  hastened  the  run-off.  Tiling  has  changed  much  upland  soil  from 
a  normally  wet,  sticky  condition  to  a  dry,  granular  substance  of  improved 
tilth,  but  at  the  same  time  a  much  more  easily  eroded  material.  Quarry- 
ing has  hastened  erosion  in  limited  areas  by  steepening  the  gradients  of 
wet-weather  streams  and  by  forming  piles  of  wasted  overburden,  subject 
to  easy  erosion. 

Clearing  of  brush  and  timber  from  the  slopes  of  Rock  River  valley 
and  its  tributaries  has  been  more  important.  On  these  steep  slopes  much 
soil  and  disintegrated  rock  have  been  released  by  the  removal  of  the  gross 
vegetation,  and  erosion  by  slope  wash,  creep  and  landslide  has  been  greatly 
facilitated.  Accelerated  erosion  is  noted  especially  where  the  St.  Peter 
formation  underlies  the  slope,  for  the  sandstone  soil  is  so  dry  that  sod  does 
not  form  readily.  Gullies  and  ravines  have  been  cut  back  into  the  upland 
as  much  as  250  feet  as  a  result  of  clearing  timber  in  the  last  50  years.  In 
some  untimbered  ravines  along  Rock  River,  the  St.  Peter  sandstone  is 
being  removed  rapidly  while  adjacent  ravines  which  are  well-timbered 
show  little  removal  of  soil  and  rock.     Since  the  timber-land  slopes  are  not 


GEOLOGIC    HISTOKY  105 

generally  arable  and  serious  erosion  of  valuable  upland  may  result  from 
clearing,  the  timber  should  not  be  taken  off. 

From  the  standpoint  of  accelerated  erosion,  man's  most  important  ac- 
tivities are  the  breaking  of  the  prairie  sod  and  the  annual  plowing.  Early 
settlers  tell  graphic  stories  of  the  difficulties  encountered  in  breaking  the  land 
for  the  first  time.  The  heavy  prairie  sod  was  a  thick,  tough  mat  of  living 
and  dead  vegetation  with  roots  extending  deep  into  the  subsoil.  This  com- 
plicated tangle  of  grass  and  roots  protected  the  entire  upland  from  erosion. 
Run-off  was  sluggish,  for  water  cannot  flow  rapidly  through  such  vege- 
tation and  the  slow-moving  water  had  neither  the  velocity  to  carry  much 
load  nor  the  opportunity  to  obtain  a  load  because  of  the  covering  of  plant 
fibers.  Because  the  water  flowed  slowly,  there  was  more  opportunity  for 
it  to  soak  into  the  soil  and  less  water  ran  off.  Streams  were  not  as  full  as 
now  and  hence  were  slower  and  less  powerful  in  attacking  their  banks  and 
beds.  The  larger  run-in  provided  more  water  for  plant  growth  during 
the  dry  season  and  insured  a  more  steady  flow  of  the  streams.  Moist  soil 
is  eroded  less  easily  than  dry  and  increased  vegetation  hinders  erosion. 
The  steady  flow  of  streams  favored  vegetation  along  their  banks  and 
many  creeks  flowed  on  a  bed  of  grass.  In  flood  time,  the  streams  removed 
all  the  load  which  was  brought  by  slope  wash.  Except  for  those  streams 
which  were  filled  by  or  aggraded  because  of  the  Wisconsin  valley  trains, 
the  flood-plains  were  small. 

When  the  sod  was  destroyed,  these  conditions  were  changed.  The 
protecting  cover  was  removed  and  run-off  quickly  eroded  the  soil  and 
overloaded  the  streams.  Run-off  was  more  rapid  and  was  greater  because 
less  water  ran  into  the  ground  or  evaporated.  Greater  run-off  gave  the 
streams  greater  velocity,  and  greater  eroding  and  transporting  power.  In 
some  places,  slope-wash  overloaded  the  smallest  wet-weather  streams  and 
the  resulting  deposition  formed  a  flood-plain ;  the  smaller  streams  carried 
too  much  silt  and  sand  to  the  larger  streams,  and  they  overflowed  their 
banks  and  aggraded  their  channels  and  flood-plains.  In  practically  all  the 
larger  valleys  these  deposits  are  still  being  formed.  During  high  water, 
the  stream  overflows  its  banks  and  spreads  clay  and  silt  over  the  surface. 
The  grass  blades  rise  through  the  mud,  and  the  new  deposit  becomes  a 
part  of  the  alluvium  of  the  flood-plain.  The  change  in  alluvial  deposits 
may  be  seen  in  many  gullies  where  the  older  fine-grained  alluvium  is 
black  with  plant  matter,  while  the  recent  overlying  silt  is  often  sandy, 
and  is  brown  instead  of  black,  because  its  rapid  deposition  does  not  per- 
mit burial  of  enough  plant  matter  to  blacken  it. 

The  annual  plowing  produces  results  similar  to  those  following  the 
original  breaking  of  the  sod.  It  destroys  the  year's  growth  of  vegetation 
and  exposes  fresh,  loose  soil  to  erosion.     Much  of  the  erosion  can  be  pre- 


106  DIXON    QUADRANGLE 

vented  by  contour  plowing  instead  of  plowing  straight  furrows  down  steep 
slopes.  Plowing  around  the  hill  provides  a  series  of  depressions  in  which 
the  run-off  must  pause  and  deposit  much  of  the  soil  it  is  carrying,  whereas 
the  furrow  running  down  the  slope  forms  a  ditch  or  channel  aiding  the  re- 
moval of  the  valuable  black  soil. 

Gullies  develop  on  steep  slopes  and  work  back  into  the  upland  by  ero- 
sion of  the  head  of  the  gully.  A  vertical  fall  of  five  feet  or  more  is  not 
uncommon  where  the  run-off  from  the  upland  enters  the  gully.  The  falling 
water  undermines  the  steep  slope  and  erodes  it  as  it  plunges  down.  A  one- 
day  rain  cut  a  gully  40  feet  back  into  the  upland  east  of  Ridge  Road.  Fur- 
ther development  of  such  ravines  can  be  checked  only  by  preventing  erosion 
at  their  heads.  This  may  be  done  by  sodding  the  gully  slopes,  by  diverting 
water  from  their  heads,  by  care  in  plowing,  or  by  building  a  dam.  A  dam 
may  fail  because  the  water  is  allowed  to  fall  over  it,  scouring  out  a  pot  hole 
below  which  may  be  so  large  that  the  dam  itself  will  tumble  into  it,  or  be- 
cause the  soil  settles  down  from  the  uphill  side  of  the  dam  and  the  wet- 
weather  stream  runs  underneath  the  structure.  Such  failure  can  be  pre- 
vented by  making  the  water  flow  down  an  inclined  concrete  face,  or  by  let- 
ting it  fall  upon  a  large  and  well  reenforced  concrete  platform  at  the  foot 
of  the  dam.  Whatever  process  is  used,  the  purpose  is  to  prevent  erosion 
at  the  danger-point,  which  is  the  head  of  the  gully  or  ravine. 


CHAPTER  V— STRUCTURAL  GEOLOGY 

General  Statement 

The  structure  of  the  Dixon  area  is  controlled  by  the  La  Salle  anticline, 
which  extends  through  the  quadrangle  from  the  center  of  its  north  side  to 
its  southeastern  corner,  and  by  the  Savanna-Sabula  anticline,  which  extends 
east- west  immediately  north  of  the  quadrangle. 

Cady1  has  described  these  features  in  their  general  relations  to  the 
structure  of  the  State.  The  present  discussion  is  an  elaboration  and  slight 
modification  of  his  work  in  the  Dixon  area.  Throughout  most  of  its  length, 
the  La  Salle  anticline  is  asymmetrical,  with  a  much  steeper  and  longer  limb 
on  the  west  than  on  the  east.  In  fact,  the  eastern  limb  dips  so  gently  that 
in  mo;-t  places  the  anticline  is  properly  describable  as  a  monocline,  using  this 
term  in  its  original  sense  of  a  steeply  dipping  series  of  strata  connecting 
two  nearly  flat  series.  From  Freeport  to  the  oil  fields  in  Crawford  and 
Lawrence  counties,  the  anticline  trends  about  S.  20°  E. 

The  Savanna-Sabula  anticline  has  been  described  along  Mississippi 
River  by  McGee,2  Savage3  and  Carman.4  Cady5  has  traced  it  eastward 
through  the  Oregon  Basin,  which,  for  the  most  part,  lies  immediately  north 
of  this  quadrangle,  although  a  portion  occupies  Kyte  River  valley  and  Rock 
River  valley  north  of  Devils  Backbone.  The  basin  is  a  result  of  the  erosion 
of  the  dome  formed  at  the  intersection  of  the  axes  of  the  La  Salle  and  Sa- 
vanna-Sabula anticlines.  Tertiary  peneplanation  exposed  the  St.  Peter 
throughout  the  basin,  and  subsequent  erosion  has  removed  much  of  the 
sandstone,  leaving  the  outward-dipping  Platteville  limestone  standing  in  an 
encircling  series  of  hills.  This  escarpment  includes  Devils  Backbone,  and 
its  continuation  southeastward  across  Rock  River  to  Lighthouse  Point,  near 
Lighthouse  School,  and  then  eastward  to  the  south  branch  of  Kyte  River. 
The  remainder  of  the  basin  rim  lies  north  and  northeast  of  this  quadrangle. 

Structure-contour  Map 

The  structure  map  (PI.  V)  indicates  graphically  the  detailed  structure 
of  the  quadrangle  by  means  of  contours  drawn  on  the  original  surface  of 

1  Cady,    G.   H.,    The   structure   of    the   La   Salle   anticline:    Illinois   State   Geol.    Sur- 
vey  Bull.    36,    pp.    89-179,    1920. 

2  McGee,    W.    J.,    Pleistocene    history    of    northeastern    Iowa:    U.    S.    Geol.    Survey 
Eleventh  Ann.  Rept.,  pt.  1,  p.  340,  1891. 

3  Savage,    T.    E.,    Geology    of   Jackson    County,    Iowa:    Iowa    Geol.    Survey,    vol.    16, 
p.    640,    1905. 

4  Carman,    J.    E.,    The    Mississippi    Valley    between    Savanna    and    Davenport:    Illi- 
nois   State    Geol.    Survey    Bull.    13,    p.    10,    1909. 

5  Op.    cit.,    p.    132. 

107 


108  DIXON    QUADRANGLE 

the  St.  Peter  sandstone.  These  structure  contours  are  similar  to  topo- 
graphic contours,  each  line  passing  through  points  of  equal  elevation  on  top 
of  the  formation.  Where  lines  are  crowded  the  dip  or  slope  is  steep ;  where 
they  are  more  widely  separated,  the  dip  is  more  gentle.  The  vertical  inter- 
val between  the  structure  contours  is  20  feet.  A  dip  of  one  degree  amounts 
to  92  feet  per  mile  and  hence  is  represented  by  approximately  four  and  a 
half  intervals  in  a  mile.  Over  almost  all  of  the  area,  the  dip  is  less  than 
40  minutes,  or  60  feet  per  mile.  Elevations  of  the  St.  Peter  surface  were 
determined  at  the  outcrop  of  the  St.  Peter-Glenwood  contact.  These  are 
represented  on  the  map  by  triangles  with  surface  elevation  stated.  Eleva- 
tions determined  by  well  records  are  indicated  by  circles  and  elevations. 
Where  the  elevation  of  the  St.  Peter-Glenwood  contact  is  known,  the  ele- 
vation of  this  surface  is  stated ;  where  the  well  was  stopped  in  Platteville 
limestone,  the  elevation  of  the  bottom  of  the  well  is  given  with  a  minus  sign, 
showing  that  the  St.  Peter  is  some  distance  below ;  where  the  well  entered 
the  St.  Peter  immediately  beneath  the  till,  the  elevation  of  the  present  top 
of  the  sandstone  is  followed  by  a  plus  sign  to  indicate  that  the  original  sur- 
face of  the  St.  Peter  was  higher  than  the  present  rock.  In  a  few  cases, 
approximate  elevations  were  calculated  from  the  surface  exposure  of  some 
higher  bed,  and  these  are  represented  by  the  quarry  symbol  and  the  calcu- 
lated elevation  of  the  St.  Peter  with  a  minus  sign  to  indicate  that  the  for- 
mation is  at  least  as  low  as  the  elevation  given,  or  a  plus  or  minus  sign  is 
used  to  call  attention  to  the  fact  that  the  figure  is  only  approximately  cor- 
rect. In  addition  to  the  points  shown  on  the  map,  the  following  elevations 
also  were  taken  into  consideration. 

Table  6. — Elevations   of  top   of  St.  Peter  sandstone  at  points   outside   the  Dixon 
quadrangle  used  in  preparing  structure  map 

Location  Elevation 

Feet 
City  water  well,  Sterling,  sec.  22,  T.  21  N.,  R.  7  E.,  about  11  miles  S.  70° 

W.  from  Dixon  -33 

Outcrops  in  NW.  14  sec.  33,  T.  21  N.,  R.   11  E.,  about  a  mile  east  of  Hart 

School 800 

Outcrops  in  SW.  %  sec.  4,  T.  22  N.,  R.  11  E.,  about  three-fourths  of  a 

mile  east  of  Prairie  View  School 745 

Outcrop  in  roadside  cut,  NW.  %  sec.  2,  T.  23  N.,  R.  10  E.,  about  1.2  miles 

northeast  of  point  where  Rock  River  enters  quadrangle 745 

Outcrop  on  hill,  NW.   %   sec.  9,  T.  23  N.,  R.  11  E.,  about  a  half  mile 

northeast  of  NE.  corner  of  quadrangle 790 

Structure  contours  are  broken  where  their  positions   are   inferred   or 
doubtful;  the  lines  are  solid  when  they  are  known  to  be  practically  accurate. 


STRUCTURAL    GEOLOGY  109 

Structure  of  the  Quadrangle 
The  crest  of  the  La  Salle  anticline  enters  the  Quadrangle  annroximatelv 


the  limestone  along  both  the  axis  and  the  western  limb  of  the  anticline,  leav- 
ing the  eastern  flank  exposed  as  an  eastward-dipping  monocline.  The  west 
dips  of  the  limestone  are  confined  to  the  SW.  Y\  sec.  26  and  not  unnaturally 


Op.    cit.,   p.    11! 


108 


DIXON    QUADKANGLE 


the  St.  Peter  sandstone.  These  structure  contours  are  similar  to  topo- 
gram* •  ~~~u  1™  ^occino-  thrnnp-h  ooints  of  equal  elevation  on  top 
oft 


the: 

val 

to  ' 

hal 

40 

det 

rej 

tio: 

W 

va 

lin 

sh 

th 

of 

fa 

ai 

hi 
la 
n 
u 
r< 
a 


Outcrop  on  hill,   jnw.   ■%   sec  6,    x.  -«.  _. 
northeast  of  NE.  corner  of  quadrangle, 


Structure  contours   are  broken   where   their  positions   are   inferred   or 
doubtful;  the  lines  are  solid  when  they  are  known  to  be  practically  accurate. 


STRUCTTTKAL   GEOLOGY  109 

Structure  of  the  Quadrangle 

The  crest  of  the  La  Salle  anticline  enters  the  quadrangle  approximately 
on  Rock  River,  extends  southwestward  almost  to  Ridge  Road,  turns  south 
and  runs  past  Grand  Detour,  and  then  turning  southeastward,  continues  to 
the  southeast  corner  of  the  quadrangle.  From  this  axis  the  strata  dip  about 
60  feet  per  mile  in  a  generally  S.  60°  W.  direction.  From  a  shallow  bi- 
furcated syncline  near  Pennsylvania  Corners,  one  arm  extends  southeastward 
toward  Grand  Detour  and  the  other  northeastward  past  Columbian  School 
to  Devils  Backbone.  The  southern  branch  is  not  marked  by  pronounced 
disturbance  of  the  strata  and  is  recognizable  only  by  study  of  the  elevations 
of  the  St.  Peter.  The  northern  syncline  is  more  evident  in  the  field.  In 
sec.  16,  T.  23  N.,  R.  9  E.,  southwest  of  Columbian  School,  local  dips  to  the 
northwest  as  high  as  14°  are  found  on  the  south  side  of  the  syncline,  and 
dips  ranging  up  to  5°  toward  the  south  occur  on  the  north  limb.  So  far 
as  outcrops  show,  none  of  these  attitudes  are  persistent  for  more  than  200 
feet,  and  the  structure  map  indicates  that  the  steep  slopes  flatten  out  within 
a  short  distance.  From  the  angle  in  the  La  Salle  anticline  crest,  near  Grand 
Detour,  a  broad  plunging  anticline  or  nose  extends  westward  down  the 
flank  of  the  main  structure.  A  minor  syncline  parallels  this  nose  on  the 
south,  while  the  better  developed  Pennsylvania  Corners-Grand  Detour  syn- 
cline lies  to  the  north. 

The  east  flank  of  the  La  Salle  anticline  is  less  regular.  The  high  area 
on  the  St.  Peter  surface  in  sees.  22  and  23,  T.  22  N.,  R.  10  E.,  has  been 
referred  to  in  the  discussion  of  the  St.  Peter-Glenwood  contact.  The 
sandy  character  of  the  overlying  limestone  and  the  thinning  out  of 
limestone  beds  against  the  sandstone  indicate  that  this  was  an  original  irregu- 
larity of  the  St.  Peter  surface  and  is  not  a  result  of  later  disturbance.  The 
depression  west  of  Lighthouse  Point  in  sees.  26  and  27,  T.  23  N.,  R.  10  W., 
may  also  represent  an  original  surface  irregularity,  but  there  is  no  evidence 
for  this  suggestion.  It  is  possible  that  a  good  exposure  in  this  basin  would 
show  a  greater  thickness  of  the  Buff  member  of  the  Platteville,  but  the  out- 
crop is  so  heavily  covered  by  till  slumping  from  above  that  this  possibility 
cannot  be  checked. 

A  narrow  anticline  with  strong  dips  extends  southeastward  from  Devils 
Backbone,  the  highest  part  of  the  structure.  CadyG  referred  to  this  feature 
as  a  monoclinal  fold,  as  it  appears  to  be  in  sees.  22  and  23,  T.  23  N.,  R.  10  E. 
Erosion  by  the  unnamed  creek  immediately  to  the  west  has  removed 
the  limestone  along  both  the  axis  and  the  western  limb  of  the  anticline,  leav- 
ing the  eastern  flank  exposed  as  an  eastward-dipping  monocline.  The  west 
dips  of  the  limestone  are  confined  to  the  SW.  T/\  sec.  26  and  not  unnaturally 

6  Op.    cit.,    p.    118. 


110  DIXON    QUADRANGLE 

were  overlooked  in  the  general  study  of  the  anticline  in  its  larger  aspects. 
The  east  limb  of  this  structure  flattens  out  in  the  mesa  in  the  center  of  sec. 
23.  Probably  the  structure  rises  northeastward  toward  the  center  of  the 
Oregon  Basin,  but  erosion  by  Kyte  River  has  destroyed  all  evidence.  The 
small  anticline  is  prolonged  southeastward  by  a  broad,  flat  area  east  of 
Carthage.  The  most  striking  feature  of  the  whole  quadrangle  structure 
is  the  compressed  syncline  in  the  southwestern  part  of  T.  23  N.,  R.  11  E. 
and  adjacent  areas.  This  structure  is  so  sharply  divergent  in  strike  and 
form  from  the  other  areas  of  the  quadrangle  that  it  was  very  carefully 
studied  in  the  field.  The  north  flank  of  the  syncline  makes  the  south  side 
of  the  Oregon  Basin,  as  already  described.  For  a  short  distance,  very  steep 
dips  occur,  amounting  in  one  case  to  30°.  The  dip  decreases  even  across 
a  50-foot  quarry  face  and  averages  only  2°  from  the  escarpment  face  to  the 
valley  on  the  south.  The  south  limb  of  the  syncline  is  not  well  exposed, 
but  its  position  is  fairly  closely  controlled  by  the  Platteville  outcrops  in  east- 
ern sec.  36,  the  St.  Peter-Glenwood  contacts  north  and  east  of  Carthage, 
and  the  outcrops  north  of  Prairie  View  School  in  sec.  5,  T.  22  N.,  R.  11  E. 

Origin  of  the  Structure 

The  following  experiment  will  show  how  the  folds  of  the  area  were  de- 
veloped. Place  a  moderately  heavy,  but  not  stiff,  cloth  on  a  table,  warp 
it  into  a  gentle  anticline  extending  N.  20°  W.  to  represent  the  La  Salle 
anticline,  and  place  weights,  such  as  books,  on  the  sides  to  hold  the  fold  in 
place.  Leave  a  few  inches  of  the  cloth  free  at  the  north  end,  and  under 
this  end  insert  a  ruler  on  an  east-west  line  to  represent  the  Savanna-Sabula 
anticline.  Now  raise  the  ruler  vertically  two  or  three  inches,  being  careful 
to  keep  it  horizontal.  If  this  is  done  carefully,  a  sharp  syncline  represent- 
ing the  Prairie  View  syncline  will  form  on  the  east,  the  axis  of  the  anticline 
will  be  bent,  so  that  south  of  the  syncline  it  will  trend  farther  west  of  north, 
and  a  high  point  will  develop  on  the  axis  north  of  the  syncline,  correspond- 
ing to  the  Devils  Backbone  which  is  apparently  the  high  point  of  the  Oregon 
Basin.  On  the  west  side  of  the  anticline  one  or  more  synclines  will  appear, 
analogous  to  the  Pennsylvania  Corners  synclines  and  a  plunging  anticline 
which  corresponds  to  the  Grand  Detour  nose  will  extend  westward  from  the 
point  of  maximum  displacement  of  the  anticline. 

The  first  event  was  the  formation  of  the  La  Salle  anticline,  perhaps,  as 
Cady7  suggests,  by  movement  along  a  deep-seated  fault.  This  structure 
has  repeatedly  been  a  zone  of  movement,  as  was  stated  in  Chapter  IV. 
Cady  has  also  pointed  out  that  the  La  Salle  and  other  areas  show  similar 
evidence  of  movement  at  several  times.  Second,  there  was  an  uplift  along 
the  Savanna-Sabula  axis.     This  may  easily  have  resulted  from  thrusting  of 


Op.    cit.,    p.    179. 


STRUCTURAL   GEOLOGY  111 

the  Wisconsin  land  mass  against  the  younger  sediments  of  the  Illinois 
basin.  Such  thrusting  necessitated  a  crumpling  of  the  earth's  strata,  if  it 
was  to  be  accommodated.  When  a  crumpling  uplift  occurred  along  an 
east-west  line,  the  beds  between  the  old  anticline  and  newly  uplifted 
fold  were  compressed,  and  in  yielding  formed  a  syncline.  They  were 
already  bowed  down  and  continued  yielding  in  the  same  way.  In  compe- 
tent rocks,  folding  may  be  localized  along  the  line  of  earliest  strain-relief, 
and  so  produce  a  compressed  structure,  like  the  Prairie  View  syncline.  As 
the  east-west  syncline  developed,  it  thrust  against  the  side  of  the  old  La 
Salle  anticline.  The  old  anticline  was  already  under  linear  compression; 
and  with  the  application  of  the  side  thrust  by  the  syncline,  the  earlier 
structure  yielded  by  permitting  displacement  of  its  axis  to  the  west.  As 
the  old  anticline  failed,  it  thrust  against  its  western  limb  at  the  point  of 
failure  and  formed  a  plunging  anticline  extending  down  the  west  limb 
from  the  newly  formed  angle  in  its  crest  line.  This  subsidiary  western 
anticline  is  the  plunging  anticline  or  nose  which  runs  northwestward  from 
Grand  Detour.  Subordinate  synclines  formed  between  the  plunging  anti- 
cline and  the  east-west  uplift  on  the  north. 

There  is  no  evidence  which  closely  defines  the  time  of  cross-folding. 
It  was  post-Galena,  since  that  formation  is  affected  equally  with  the 
others,  and  was  pre-Tertiary,  for  the  Tertiary  peneplain  bevels  all  the  struc- 
tures. 

Pre-St.  Peter  Structure 

At  several  small  outcrops  in  a  valley  tributary  to  Franklin  Creek  (NW. 
%  sec.  33,  T.  22  N.,  R.  10  E.),  Shakopee  dolomite  is  exposed  with  very 
steep  dips  and  widely  varying  strike.  Another  outcrop  in  sec.  9,  T.  23  N., 
R.  10  E.  shows  a  12°  dip  to  the  northeast  for  about  120  feet.  It  is 
possible  that  these  beds  indicate  pre-St.  Peter  folding,  but  the  writer 
regards  them  as  more  probably  a  result  of  slumping  incidental  to  the  deep 
erosion  that  preceded  the  St.  Peter.  The  very  large  Shakopee  area  in 
Franklin  Creek  shows  no  disturbance  and  several  exposures  near  the  steeply 
dipping  beds  in  the  Franklin  Creek  tributary  are  not  much  distorted  (fig. 
11).  Other  large  outcrops  one,  three  and  four  miles  north,  show  no  dip 
exceeding  5°  and  the  principal  outcrops  west  of  Rock  River  are  of  flat- 
lying  strata.  If  pre-St.  Peter  folding  occurred,  it  failed  to  disturb  most 
of  the  strata,  and  its  character  and  amount  are  indeterminable. 

Faulting 

The  only  fault  recognized  in  the  area  is  located  in  the  SE.  %  NE.  T4 
sec.  16,  T.  23  N.,  R.  9  E.,  on  the  south  bank  of  Pine  Creek.  It  strikes  N. 
25°  W.,  dips  70°  W.,  and  has  a  normal  downthrow  on  the  west  of  30 
inches. 


CHAPTER   VI— MINERAL   RESOURCES 
General    Statement 

The  preceding  chapters  have  discussed  the  origin  and  history  of  the 
rocks  of  the  area.  In  this  chapter,  the  value,  distribution  and  amount 
of  the  mineral  resources  will  be  considered.  Mineral  resources  are  use- 
ful rocks  or  useful  substances  that  can  be  obtained  from  the  rocks.  The 
demand  for  most  substances  determines  their  selling  price,  and  the  value 
of  most  mineral  resources  depends  upon  the  difference  between  the  price 
obtained  and  the  cost  of  production.  The  value  in  place  is  small,  for 
supplies  are  generally  abundant,  and  the  selling  price  is  only  a  little  greater 
than  the  cost  of  production.  For  instance,  the  cost  of  coal  delivered  in 
a  bin  consists  chiefly  of  costs  of  mining,  transportation  and  marketing, 
and  of  profits  on  these  operations.  In  the  ground,  the  coal  commonly 
sells  for  less  than  20  cents  per  ton. 

In  one  sense,  soil  is  a  mineral  resource,  for  it  is  a  mixture  of  fresh 
and  decayed  rock  matter  with  plant  substances,  but  because  it  is  the  basis 
of  agriculture  and  is  inextricably  connected  with  plant  and  animal  growth, 
it  is  not  usually  considered  in  discussions  of  mineral  resources. 

In  this  area,  the  principal  mineral  resources  are  water,  cement  mate- 
rials, limestone  and  its  products,  glass  sand,  and  building  sand  and  gravel. 
Potential  resources  of  potash  occur  and  unimportant  traces  of  natural  gas, 
petroleum  and  some  ore  minerals  have  been  reported.  Of  the  resources  now 
developed,  ample  and  cheap  supplies  are  available  for  all  industries,  ex- 
cept cement  making.  The  area  contains  an  abundance  of  cement  materials, 
but  most  of  this  cannot  be  secured  at  a  reasonable  cost. 

Water 

SURFACE  WATER 

Both  surface  and  ground  waters  are  important  resources  in  most 
regions.  Water  is  essential  to  all  forms  of  life  and  a  steady  supply  of  pure 
water  is  one  of  man's  fundamental  needs  in  any  place.  None  of  the  sur- 
face waters  within  the  quadrangle  is  important  for  drinking  or  manu- 
facturing purposes.  Most  of  the  streams  are  dry,  or  nearly  so  in  late 
summer.  Rock  River  and  five  of  its  tributaries,  Kyte  River,  and  Clear, 
Franklin,  Chamberlain  and  Pine  creeks,  are  the  only  streams  that  can  be 
depended  upon  for  a  flow  exceeding  10  gallons  per  minute  throughout  the 

112 


WATEE  113 

year.  Their  waters  are  so  turbid,  because  of  the  overloaded  condition 
resulting  from  the  present  rapid  erosion,  that  they  could  not  be  used 
for  domestic  or  boiler  purposes  without  expensive  treatment. 

The  only  water-power  utilized  is  obtained  from  Rock  River  at  Dixon, 
where  Platteville  limestone  outcrops  in  the  present  bed  of  the  stream  and 
rapids  have  developed.  Probably  North  Dixon  stands  on  the  filling  of  the 
old  stream  channel,  for  bed  rock  is  over  60  feet  lower  within  a  mile,  both 
up  and  down  stream.     The  limestone  affords  an  excellent  foundation. 

Additional  power  could  be  developed  by  a  dam  near  Grand  Detour. 
Like  the  Dixon  property,  the  head  would  be  low,  for  Rock  River  falls  an 
average  of  only  0.9  feet  per  mile  and  the  dam  in  Oregon  is  not  20  feet  above 
normal  river  level  in  Grand  Detour. 

GROUND  WATER 

In  this  area,  ground  water  is  of  economic  importance  as  the  source  of 
shallow  and  artesian  wells,  springs  and  water  for  plant  growth. 

WATER  FOR  VEGETATION 

Growing  plants  receive  an  adequate  quantity  of  water  throughout  the 
area,  except  in  sand-dune  areas  and  on  the  higher  outcrops  of  the  St.  Peter 
sandstone.  In  these  places,  the  ground- water  table  may  be  so  deep  that  only 
very  hardy  or  long-rooted  plants  can  live.  Because  of  its  high  porosity,  the 
St.  Peter  contains  abundant  water  near  the  level  of  the  streams,  but  the 
ground-water  table  is  nearly  horizontal  and  lies  far  below  the  hill  tops. 
Where  glacial  till  still  covers  the  surface,  there  is  abundant  ground  water 
in  the  till  and  vegetation  is  normal ;  but  closer  to  Rock  River  and  near  the 
main  creeks,  the  sandstone  forms  the  hills  and  valleys.  The  aridity  of  St. 
Peter  outcrops  has  produced  a  curious  assemblage  of  desert  plants  in  a  re- 
stricted area  between  Franklin  Creek  and  the  southern  line  of  Nashua 
Township.  There,  the  clumps  of  dry  rustling  grass,  cactus,  and  sand  burrs 
scattered  over  the  sandy,  glistening  plateaus,  and  the  miniature,  flat-topped, 
vertical-sided  mesas  combined  with  a  desert  fauna,  are  typical  on  a  small 
scale  of  the  sand  wastes  of  Arizona. 

SPRINGS 

The  contact  of  the  Platteville  with  the  underlying  Glenwood  is  marked 
by  springs,  outlining  the  limestone  boundary,  even  in  places  where  it  is 
thoroughly  covered.  Water  traveling  downward  through  the  limestone  can- 
not pass  through  the  shale,  and  so  moves  along  it  laterally,  later  appearing 
in  springs,  such  as  those  along  the  bluffs  of  Rock  River  near  Lowell  Park, 
and  along  Pine  Creek,  Sevenmile  Branch  and  the  southern  tributaries  of 
Kyte  River.  Some  of  these  springs  fail  in  late  summer,  but  most  of  those 
which  have  much  Platteville  limestone  above  to  draw  from  flow  throughout 


114  DIXON    QUADRANGLE 

the  year.  Where  the  limestone-shale  contact  passes  through  a  hill,  springs 
are  more  common  on  the  hill-side  toward  which  the  strata  dip,  and  such 
springs  are  normally  perennial.  The  largest  Glenwood-Platteville  spring 
in  the  quadrangle  is  located  in  sec.  12,  T.  22  N.,  R.  10  E.,  and  has  a  flow 
of  about  400  gallons  per  minute  in  late  August.  In  addition  to  the  Glen- 
wood-shale  springs,  three  springs  issue  from  the  Shakopee  dolomite  in 
Franklin  Creek  valley.  One  of  the  springs  from  the  Shakopee  carries  much 
iron,  which  is  deposited  around  the  spring  as  limonite.  With  this  exception, 
all  the  springs  of  the  quadrangle  supply  palatable  water.  No  spring  in  this 
quadrangle  is  known  to  be  polluted,  but  the  sink  holes  in  the  Platte ville  are 
evidence  of  large  underground  channels,  and  some  of  the  springs  may  be 
supplied  from  such  a  source.  Spring  water,  therefore,  is  not  necessarily 
pure  and  safe  for  drinking. 

SHALLOW  WELLS  IN  TILL 

Wells  less  than  200  feet  deep  are  common  and  easily  drilled.  They  are  of 
four  general  types,  drawing  water  from  till,  alluvium,  limestone,  or  the  St. 
Peter  sandstone.  The  wells  drilled  in  the  till  are  the  most  common,  and 
range  from  15  to  185  feet  in  depth.  In  the  till,  irregular  patches  and  layers 
of  sand  occur,  which  are  chiefly  stream  deposits  and  small  out  wash  plains 
later  overridden  by  a  short  advance  of  the  ice.  Irregular  joint  planes  also 
traverse  the  till,  and  water  follows  these  channels  closely.  On  cliff  expos- 
ures of  the  till,  the  joints  may  often  be  seen,  marked  by  staining  and  leach- 
ing by  the  water.  Their  origin  is  uncertain,  but  may  be  due  to  the  fact 
that  the  till  is  not  an  ordinary  clay,  but  contains  so  much  rock  flour  that  it 
has  a  tendency  to  cement  together  and  crack  like  other  sediments.  More 
commonly,  the  till  water  comes  from  sand  lenses  of  uncertain  extent.  Their 
irregularity  is  attested  by  the  number  of  dry  holes  which  have  been  drilled 
on  some  farms  before  a  good  well  was  secured.  The  till  is  never  dry  in 
depth,  but  the  water  may  seep  out  so  slowly  that  the  well  is  unsatisfactory 
and  is  called  dry.  Because  of  the  uncertain  size  of  the  sand  lenses,  the 
driller  always  tests  the  well  by  pumping  at  a  rate  much  greater  than  normal- 
ly will  be  required.  If  the  test  pump  fails  to  lower  the  water,  it  is  being 
supplied  as  fast  as  pumped,  and  the  well  is  pronounced  a  success. 

Till  wells  bored  or  dug  during  the  early  settlement  of  the  area  have 
been  deepened  an  average  of  20  feet.  The  greater  depth  may  have  been 
necessary  in  part  to  secure  a  larger  supply  of  water  because  of  the  increased 
demands  of  the  modern  stock  farm,  but  drillers  agree  that  it  is  necessary 
to  go  deeper  than  formerly  to  get  a  good  well.  Deeper  drilling  has  been 
made  necessary  by  the  lowering  of  the  ground- water  table.  Some  drillers 
estimate  that  the  lowering  of  the  water  surface  amounts  to  35  feet.  Accu- 
rate data  are  not  available.     Well  records  do  not  furnish  good  evidence,  for 


WATER    WELLS  115 

the  demand  on  the  wells  may  have  reduced  the  water  table  locally ;  but  it 
seems  probable  that  the  general  water  level  is  at  least  20  feet  lower  than  it 
was  60  years  ago.  The  great  increase  in  run-off,  which  has  accelerated  the 
rate  of  erosion,  has  reduced  the  opportunity  for  run-in,  decreased  the  amount 
of  ground  water,  and  accordingly  lowered  the  ground-water  table. 

The  only  artesian  well  reported  in  the  glacial  drift  was  drilled  near  the 
northwest  corner  of  sec.  9,  T.  23  N.,  R.  10  E.  near  Tealls  Corners.  This 
well  was  made  by  driving  a  two-inch  pipe  18  feet  into  the  ground.  For 
several  years  water  flowed  with  a  head  of  about  two  feet  above  the  surface. 
In  deepening  the  well  to  increase  the  flow,  the  St.  Peter  sandtsone  was  en- 
countered, the  water  escaped  downward  into  the  sandstone,  and  the  well  was 
ruined. 

WELLS   IN   LIMESTONE 

Many  wells  in  the  limestone  area  pass  through  the  overlying  soil  or  till 
without  encountering  a  satisfactory  supply  of  water,  and  are  then  drilled 
into  the  limestone.  Like  the  till,  the  limestone  may  be  saturated  and  yet  the 
water  may  not  flow  into  a  well  fast  enough  to  satisfy  the  demand.  There 
are  no  sand  layers  in  the  limestone,  but  it  is  traversed  by  many  joint  planes. 
Water  travels  along  these  planes  very  freely,  in  many  places  dissolving  the 
rock  to  form  large  channels,  and  the  well  that  strikes  one  of  them  will  have 
an  abundance  of  water.  Because  water  travels  so  readily  through  the  lime- 
stone it  is  not  filtered  and  may  be  highly  dangerous.  The  sink  holes  de- 
scribed in  Chapter  IV  are  the  result  of  water  dissolving  the  limestone  as  it 
passes  through.  Rubbish  thrown  into  these  holes  drains  into  the  water 
channel  and  may  supply  highly  dangerous  water  to  wells  a  long  distance 
away.  Good  water  may  sometimes  be  obtained  from  limestone,  but  it  is 
always  subject  to  suspicion,  and  should  not  be  drunk  if  its  taste,  color  or 
odor  is  peculiar.  Freedom  from  peculiar  smell  or  taste,  however,  does  not 
prove  that  it  is  pure. 

The  analysis  cited  below  shows  the  fallacy  of  the  popular  idea  that  a 
deep  well  has  pure  water.  This  well  is  deeper  than  95  per  cent  of  the  wells 
in  the  quadrangle,  but  the  high  chlorine  and  very  high  nitrate  content  prove 
that  the  well  is  contaminated  with  sewage.  No  uncurbed  well  is  necessa- 
rily safe  because  it  is  deep  and  limestone  wells  are  especially  dangerous. 
This  water  is  not  drunk,  but  is  used  in  the  power  plant. 

Water  is  retained  in  the  limestone  by  the  underlying  Glenwood  shale 
at  many  places  where  the  contact  between  the  formations  lies  well  above  the 
adjacent  drainage  lines.  If  the  water  were  free  to  move  downward  into 
the  St.  Peter  formation,  it  would  soon  be  drained  away.  Several  limestone 
wells  have  been  ruined  by  drilling  them  too  deep,  penetrating  the  sandstone, 
and  thus  permitting  the  water  to  escape  from  the  bottom  of  the  well. 


116  DIXOX    QUADRANGLE 

The  following  analysis  shows  the  character  of  the  water  in  a  200-foot 
well  at  Dixon  State  Hospital.  The  analysis  (Lab.  No.  42,296)  was  made 
by  the  Illinois  State  Water  Survey,  Dec.  16,  1919. 

Table  7. — Analysis    of    water    in   200-foot   well   at   Dixon    State   Hospital 

Parts  per  million 

K  and  Na potassium  and  sodium 7.92 

NH4 ammonia 0.00 

N02 nitrogen  peroxide   .008 

Mg magnesium    31.36 

Ca. . . . . calcium 68.44 

Fe iron 0.00 

N03 nitrate    35.43 

CI "chlorine 11.00 

S04 sulphate   13.36 

HC03 carbonic  acid   334.28 

AL03 alumina    1.4 

S*02 silica     15.6 


Total 518.798 

The  analysis  shows  about  30  grains  per  gallon  of  dissolved  matter,  or 
20  grains  of  residue  on  evaporation,  as  compared  with  14  for  Rock  River 
and  18  for  Croixan  water.  Although  the  bottom  of  this  well  is  in  St.  Peter, 
it  is  not  curbed  or  cased,  and  the  water  has  come  largely  from  Platteville 
and  Galena  limestones,  and  is  essentially  a  limestone-well  water.  The  high 
lime  and  magnesia  with  low  soda  and  potash  are  typical  of  limestone  waters, 
as  are  also  high  carbonate  and  low  sulphate  content. 

WELLS   IN   THE  ST.   PETER  SANDSTONE 

For  shallow  wells,  the  most  consistent  water-yielding  stratum  is  the 
St.  Peter  sandstone.  Whenever  a  well  penetrates  the  sandstone  to  the  depth 
of  Rock  River,  an  abundance  of  excellent  soft  water  is  obtained.  Even 
where  the  water  comes  from  surface  drainage,  it  is  thoroughly  filtered  and 
purified  in  traveling  through  the  sand.  Away  from  Rock  River,  water  may 
be  obtained  at  higher  elevations,  and  as  a  rule,  except  within  three  miles 
of  the  river,  wells  in  the  St.  Peter  need  not  be  drilled  more  than  ten  feet 
below  the  level  of  the  nearest  valley,  even  though  it  does  not  contain  a  per- 
manent stream.  No  artesian  wells  obtain  water  from  the  St.  Peter  in  this 
quadrangle,  but  farther  from  the  outcrop,  it  yields  abundant  flows  through- 
out an  area  in  Illinois  bounded  by  Chicago,  Peoria,  and  St.  Louis.  Further 
discussion  of  St.  Peter  water  supplies  may  be  found  in  Leverett's1  paper  on 
Illinois  water  resources. 


1  Leverett,    Frank,    Water    resources    of    Illinois:    U.    S.    Geol.    Survey    Seventeenth 
Ann.   Rept.,   pp.    695-849,    1896. 


WATER    WELLS  117 

WELLS   IN  ALLUVIUM 

The  success  of  a  well  in  alluvium  depends  upon  the  ground-water  level 
and  the  composition  of  the  alluvium.  Where  the  alluvium  is  a  valley  train, 
as  in  Rock  and  Kyte  river  valleys,  it  consists  of  sand  and  gravel  and  a  well 
reaching  below  stream  level  will  have  abundant  water.  Valleys  in  the  St. 
Peter  usually  have  a  sandy  alluvium  also,  and  wells  there  obtain  plenty  of 
water.  In  limestone  areas,  the  alluvium  may  be  largely  clay,  and  it  is  then 
necessary  to  penetrate  the  underlying  limestone  to  get  water.  Water  from 
alluvium  is  usually  good ;  the  principal  drawback  to  these  wells  is  the  liabil- 
ity to  damage  and  contamination  through  flooding  of  the  lowland  in  which 
they  are  situated. 

ARTESIAN   WELLS 

Wells  in  which  water  rose  above  the  surface  of  the  ground  under  nat- 
ural pressure  were  first  drilled  in  the  department  of  Artois,  France,  and  so 
were  called  artesian.  By  an  extension  of  the  term,  any  well  in  which  water 
rises  a  considerable  distance  above  the  original  containing  stratum  is  called 
artesian,  whether  the  water  flows  at  the  surface  or  not.  In  this  area,  six 
artesian  wells  produce  water  from  the  Croixan  series. 

The  conditions  necessary  for  a  flowing  artesian  well  are  (1)  a  porous 
rock  to  carry  the  water,  (2)  an  impervious  overlying  formation  to  retain 
the  water  under  pressure,  (3)  an  outcrop  of  the  porous  rock  at  a  point 
higher  than  the  top  of  the  well,  (4)  an  adequate  supply  of  water  at  the 
outcrop  or  intake  area,  and  (5)  no  outlet  lower  than  the  well  sufficiently 
large  to  permit  all  the  water  from  the  intake  area  to  escape. 

The  Croixan  series  underlying  the  Dixon  area  meets  all  these  require- 
ments (fig.  15).  The  sandstones  furnish  the  porous  rock  outcrop  in 
central  and  southern  Wisconsin  at  a  higher  elevation  than  the  surface  of  the 
Dixon  area  and  numerous  lakes  on  the  outcrop  supply  all  the  water  that  can 
be  absorbed ;  the  Prairie  du  Chien  formation  with  its  interbedded  shales  pro- 
vides an  impervious  cover,  and  there  is  no  lower  outlet. 

Artesian  wells  supply  the  water  for  the  municipal  system  in  Dixon  and 
at  the  Dixon  Epileptic  Colony.  The  Dixon  Water  Company  has  drilled 
four  artesian  wells  to  depths  of  1610,  1720,  1765  and  1860  feet,  the  deepest 
reaching  1250  feet  below  sea  level.  The  water  from  these  wells  will  rise 
eight  feet  above  the  surface,  but  the  rate  of  flow  is  too  slow  to  supply  the 
city,  and  the  wells  are  all  pumped  to  secure  a  larger  quantity.  Two  wells 
at  the  Dixon  Epileptic  Colony  in  sec.  21,  Dixon  Township  are  1900  and 
2217  feet  deep,  the  deeper  one  extending  1415  feet  below  sea  level.  The 
water  rises  within  four  feet  of  the  surface,  or  128  feet  higher  than  in  the 
water  company's  wells,  the  Colony  wells  being  located  110  feet  higher  than 
those  in  Dixon. 

No  other  deep  artesian  wells  qre  known  in  the  quadrangle ;  others 
nearby  are  those  supplying  the  municipal  systems  in  Sterling,  Oregon,  and 


118 


DIXON    QUADRANGLE 


•fliP-ii, 


'■'.{■&> 


Dixon 


Green  River 


L.::l 


If 


w  n 


CO     ^ 


Princeton 


if 


aisl 


3     " 


?m 


m 


Vvl 


: 


CEMENT    MATERIALS  119 

Amboy.  A  large  supply  of  water  from  this  source  can  be  obtained  at  any 
point  in  this  area,  where  the  need  is  sufficient  to  justify  the  expense. 

The  depth  of  an  artesian  well  will  vary  from  1600  feet  at  the  northern 
border  of  the  quadrangle,  to  1900  feet  at  the  southern.  The  amount  of 
water  obtainable  from  any  one  well  will  depend  upon  the  size  of  the  hole 
and  the  rate  at  which  it  is  pumped.  Where  more  than  one  well  becomes 
necessary,  later  wells  should  be  placed  along  an  east-west  line  so  as  not  to 
interfere  with  one  another,  since  the  underground  movement  is  from  the 
north.  They  should  be  at  least  600  feet  apart,  or  should  vary  in  depth  by 
200  feet  or  more.  If  the  bottoms  of  the  wells  are  too  close  together  in  the 
same  horizon,  they  will  be  taking  water  from  the  same  limited  rock  mass ; 
but  by  spacing  them  more  widely,  or  by  varying  the  depths,  each  well  will 
be  supplied  from  an  independent  body  of  rock,  and  the  total  flow  will  be 
much  greater. 

Water  from  such  wells  is  of  necessity  healthful,  for  all  organic  matter 
is  filtered  out  in  the  years  the  water  spends  en  route  from  the  point  where 
it  enters  the  sand  in  south-central  Wisconsin.  The  following  analysis  of 
Dixon  city  water,  which  is  the  Croixan  artesian  water,  was  made  by  the 
Dearborn  Chemical  Company  of  Chicago  for  the  Northern  Illinois  Utilities 
Company  and  is  published  through  the  courtesy  of  the  latter  company. 

Table  8. — Analysis  of  Croixan  water  from  Dixon,  Illinois 

Parts  per  million 

Si02 silica    3.0 

Fe.03  and  A1203 ferric   oxide   and    alumina 1.6 

CaCO:! calcium   carbonate    149.4 

CaS04 calcium   sulphate    Trace 

MgCO. magnesium    carbonate 123.8 

Na2S04  and  K,S04 sulphates  of  soda  and'  potash 16.7 

NaCl  and  KC1 chlorides  of  soda  and  potash 10.2 

Loss,    etc 2.9 


Total 307.6 

This  analysis  indicates  that  the  Croixan  water  contains  about  60  per 
cent  as  much  dissolved  matter  as  a  water  from  limestone  in  this  area. 

Cement  Materials 

Portland  cement  is  made  from  an  artificial  mixture  of  limestone,  chalk, 
or  marl,  with  impure  limestone,  clay,  shale,  slate  or  slag.  Correct  propor- 
tions of  these  materials  are  finely  ground  ;  calcined  until  fusion  begins  ;  the 
resulting  clinker  is  cooled,  ground  to  flour-like  fineness;  mixed  with  a  re- 
tarder,  and  placed  on  the  market.     The  raw  materials  may  be  any  of  the 


120 


DIXOH    QUADRANGLE 


substances  listed  if  they  contain  lime,  silica,  alumina  and  iron  in  the  desired 
proportions  and  do  not  contain  too  much  sulphur  and  magnesium.  Mag- 
nesium is  highly  objectionable,  and  raw  materials  are  carefully  and  contin- 
ually being  analyzed  to  guard  against  its  presence  in  excessive  amount. 

The  Dixon  area  contains  satisfactory  limestone  in  the  fossiliferous 
Blue  and  most  of  the  Glass  Rock  members  of  the  Platteville.  Loess  is  the 
only  commercial  source  of  alumina,  silica  and  iron.  The  limestones  and 
dolomites  of  the  Prairie  du  Chien.  Burt  and  Lowell  Park  members  of  the 
Platteville.  and  the  Galena  dolomite  are  all  too  magnesian  to  be  used.  The 
Glenwood  shale  is  too  thin  to  be  a  commercial  source  of  clay  for  cement 
manufacture.  Glacial  till  has  a  suitable  composition,  but  the  cost  of  remov- 
ing boulders  and  gravel,  followed  by  extremely  tine  grinding  of  the  hard 
quartz-sand  grains   is  prohibitive.     Loess,  being  largely  the   liner  material 


Fig'.  16.    Quarrying   of  the   Blue  limestone   at   the   plant   of  the   San- 
dusky Cement  Company. 


of  the  till  already  sorted  by  streams  and  deposited  by  winds,  is  very  satis- 
factory. 

The  Sandusky  Cement  Company  has  located  its  plant  beside  Rock 
River  two  miles  northeast  of  Dixon,  where  the  full  thickness  of  the  non- 
magnesian  Blue  limestone  is  available  without  a  capping  of  Lowell  Park  or 
higher  dolomites  which  would  have  to  be  wasted  because  of  their  content 
of  magnesia.  Overlying  the  limestone  is  a  mantle  of  till  ranging  up  to  25 
feet  in  thickness  which  is  stripped  away  and  dumped  into  a  nearby  ravine. 
Above  the  till  lies  the  loess  with  a  maximum  thickness  of  15  feet.  The 
quarry  is  worked  in  three  benches.  Steam  shovels  standing  on  the  Burt 
limestone  remove  the  Blue  member  as  it  is  blasted  loose  i  fig.  16),  and  load 


CEMENT   MATERLALS 


121 


it  into  cars  for  transportation  to  the  mill.  The  limestone  shovels  often 
work  at  a  face  50  feet  high.  On  the  next  bench  above,  other  shovels  strip 
the  till,  which  is  from  4  to  25  feet  thick,  and  load  it  into  cars  to  be  hauled 
away  and  dumped.  The  top  of  the  till  forms  the  third  bench,  and  work- 
ing from  this  level,  other  shovels  strip  the  loess  and  load  it  for  transporta- 
tion to  the  mill.  The  loess  varies  in  thickness  from  1  to  15  feet,  with  an 
average  of  4*/2  feet.  Each  bench  is  kept  well  in  advance  of  the  one  beneath 
so  that  neither  caving  ground  nor  heavy  rains  can  mix  the  materials  (fig.  17) . 


Fig.  17.  Quarry  of  the  Sandusky  Cement  Company,  showing  the  quarry  face, 
the  limestone  below,  the  till  behind  the  rigs  which  drill  holes  for  blasting, 
and  a  thin  bed  of  loess  above  the  till. 


The  limestone  and  loess  are  taken  to  the  mill  where  the  loess  is  sampled, 
dried,  and  stored  until  it  is  needed  for  making  up  the  "mix"  (fig.  18). 
The  limestone  passes  through  two  jaw  crushers,  and  then  to  hammer  mills 
where  it  is  broken  into  pieces  less  than  one  twenty-fifth  of  an  inch  in  diam- 
eter. It  is  then  dried  and  passed  to  storage  bins  from  which  it  is  drawn  as 
operations  require,  mixed  with  the  loess  and  ground  until  more  than  92  per 
cent  of  the  mixture  will  pass  a  screen  having  L0,000  meshes  to  the  square 
inch.  Sieves  for  testing  this  material  are  so  fine  that  they  will  hold  water. 
The  "mix"  is  fed  into  the  kilns,  where  it  is  calcined  until  it  forms  a  clinker 
or  slag-like  mass.     To  this  clinker  about  two  per  cent  of  gypsum  is  added. 


122  DIXON    QUADKANGLE 

Gypsum  delays  the  setting  of  the  cement  and  makes  the  handling  and  work- 
ing of  concrete  mixtures  and  cement  mortars  possible  for  nearly  an  hour 
after  the  water  has  been  added.  The  clinker  and  gypsum  are  ground  to- 
gether, sacked,  and  the  resulting  cement  is  ready  for  market. 

Additional  supplies  of  cement  materials  may  be  found  in  sees.  15  and 
16,  Dixon  Township,  in  the  till-covered  area  northeast  of  Franklin  Grove, 
and  less  probably  along  Ridge  Road  in  sees.  24,  25,  35,  and  36.  In  each 
case,  unless  the  overlying  till  is  more  than  25  feet  thick,  the  non-magnesian 
part  of  the  Platteville  has  a  thickness  ranging  up  to  35  feet.  There  are  no 
other  extensive  areas  known  where  the  Blue  limestone  forms  the  surface, 
and  so  can  be  quarried  profitably.  Where  the  Lowell  Park  member  is 
present,  it  would  be  necessary  to  remove  it  first,  and  to  discard  it  because 
of  its  high  content  of  magnesia.  The  thickest  loess  deposits  are  east  of 
Rock  River,  south  of  Grand  Detour. 
\ 


Fig.  18.    The  mill  at  the  plant  of  the  Sandusky  Cement  Company. 

Limestone  and  Limestone  Products 

The  limestones  of  the  quadrangle  are  valuable  also  for  lime,  building 
stone,  road  metal  and  crushed  limestone  for  agricultural  purposes.  When 
the  region  was  first  settled,  many  quarries  were  opened,  with  lime  kilns 
beside  them  for  burning  lime.  As  long  as  timber  was  available  along  the 
streams  for  fuel,  and  freights  were  high,  this  was  profitable.  Cement  has 
largely  replaced  lime  for  building  purposes,  because  of  its  greater  strength 
and  weather  resistance,  and  there  are  now  no  active  kilns  in  the  quadrangle. 
Such  lime  as  is  still  used  is  shipped  in  from  large  plants  where  cheap  fuel 
is  available. 

From  the  Platteville,  a  magnificent  blue-gray  limestone  formerly  was 
quarried  and  used  for  many  of  the  public  buildings  in  Dixon  and  Ashton. 


LIMESTONE    AND    LIMESTONE    PRODUCTS  123 

The  stone  makes  an  excellent  appearance,  although  it  is  said  to  fade  on  long 
exposure  to  weather.  The  principal  quarries  were  on  Ravine  Road,  Dixon ; 
in  sees.  3  and  27,  Dixon  Township;  at  Lighthouse,  Nashua  Township, 
(T.  23  N.,  R.  10  E.),  and  in  sec.  23,  China  Township  (T.  22  N.,  R.  10  E.). 
While  the  Platteville  has  furnished  the  favorite  building  stone,  some  Shako- 
pee  has  been  quarried  along  Franklin  Creek  and  used  in  Franklin  Grove. 
Because  of  the  shaly  character  of  the  limestone,  there  was  too  much  waste 
in  the  quarrying  to  make  it  profitable. 

The  Galena  furnishes  a  very  satisfactory  dimension  block,  but  is  not 
favored  for  buildings,  as  it  readily  absorbs  moisture,  and  renders  the  in- 
teriors damp.  It  has  been  quarried  extensively,  however,  for  bridge  abut- 
ments and  similar  uses  by  the  Illinois  Central  Railroad  along  its  route, 
both  north  and  south  of  Rock  River.  A  large  quarry  in  the  Galena  and 
Lowell  Park  member  of  the  Platteville  was  opened  along  River  Road, 
Dixon.  Part  of  the  quarrying  was  solely  to  make  room  for  the  road,  and 
for  buildings  along  the  bluff  line.  How  much  of  the  rock  was  used  for 
building  purposes  is  not  known.  In  spite  of  its  high  porosity,  freezing  and 
other  types  of  weathering  have  only  a  slight  effect  upon  the  Galena  dolo- 
mite and  it  retains  a  fresh  appearance  for  years.  Concrete  and  brick 
have  largely  displaced  stone  for  building,  and  at  the  present  time  no  quar- 
ries are  working  out  building  stone. 

Small  amounts  of  limestone  are  crushed  by  farmers  locally  for  use 
in  their  fields.  Limestone  neutralizes  the  acids  produced  by  the  decom- 
position of  plant  remains,  which  make  soil  sour,  hindering  or  preventing 
the  growth  of  vegetation,  especially  of  such  essential  leguminous  crops 
as  clover  and  alfalfa.  An  unleached  limestone  soil  is  generally  very  fer- 
tile, provided  it  does  not  contain  an  excess  of  lime.  Limestone  is  slightly 
soluble  in  water,  and  rain  water  soaking  into  the  soil  dissolves  the  limestone 
and  carries  it  away.  Accordingly,  a  limestone  may  be  overlain  by  several 
feet  of  clay  from  which  all  the  original  lime  has  been  removed  and  the 
resulting  soil  is  sour  and  poor.  One  of  the  great  benefits  of  glaciation 
was  that  practically  all  the  worn-out  and  leached-out  soils  in  this  area 
were  removed  or  ground  up  with  crushed  limestone  and  other  rocks,  produc- 
ing one  of  the  most  fertile  soils  in  the  United  States.  On  much  of  the 
flat  land,  however,  leaching  has  removed  the  limestone  content  of  the  sur- 
face till  since  the  Illinoian  glaciation,  and  a  less  favorable  soil  is  found 
than  in  the  areas  covered  by  the  last  (Wisconsin)  glaciation  to  the  north 
and  east.  It  is  necessary  to  treat  this  land  with  limestone,  and  many  car- 
loads of  crushed  limestone  are  hauled  into  this  area  yearly. 

The  local  limestone  is  as  good  as  any  that  is  imported  and  better 
than  much  of  it.  The  value  of  limestone  depends  upon  its  content  of  cal- 
cium and  magnesium.     One  unit  of  either  metal   neutralizes   another   unit 


124  DIXON    QUADRANGLE 

of  certain  acids.  It  follows  then  that  all  impurities  in  limestone  are 
simply  inert  matter,  and  the  money  and  time  spent  for  freight,  hauling 
and  distribution  of  the  impurities  is  dead  loss.  Ten  per  cent  of  clay  in 
a  limestone,  which  is  not  an  unusual  amount,  means  that  one  load  in  ten 
is  wasted.  The  purity  of  limestone  should  therefore  be  carefully  consid- 
ered in  purchasing  it.  None  of  the  Galena  or  Platteville  limestone  analyses 
available  show  10  per  cent  impurity,  and  it  is  safe  to  regard  any  local  lime- 
stone, except  the  Prairie  du  Chien,  as  pure  enough  to  be  valuable. 

The  acid-neutralizing  power  of  limestone  varies  with  the  amount  of 
lime  and  magnesia.  A  pure  dolomite  has  108.8  per  cent  of  the  acid- 
neutralizing  power  of  a  pure  limestone,  and  is  therefore  worth  nearly  nine 
per  cent  more.  All  of  the  Galena  and  most  of  the  upper  Platteville  is 
dolomite:  the  Buff  limestone  of  the  Platteville  is  highly  magnesian,  but 
not  actually  a  dolomite.  It  follows,  then,  that  the  limestone  occurring  im- 
mediately above  the  St.  Peter,  which  is  the  Buff  limestone,  the  upper  Platte- 
ville and  all  of  the  Galena  are  the  most  desirable  agricultural  limestones. 
Whether  the  extra  nine  per  cent  of  acid-neutralizing  power  is  worth  a 
special  effort  to  secure  it  depends  upon  the  individual  case.  There  is 
abundant  limestone  for  all  agricultural  needs :  any  limestone  outcropping 
in  the  area  of  the  Platteville  or  Galena  formations  will  be  satisfactory. 

The  most  important  use  now  being  made  of  limestone  in  the  quadrangle 
is  for  road  metal.  Limestone  is  so  widely  distributed  over  the  area  that 
a  new  quarry  can  be  opened  in  many  cases  more  cheaply  than  the  stone  can 
be  hauled  from  an  existing  pit.  The  amount  of  stripping  is  usually  slight ; 
a  place  where  rock  is  already  exposed  in  a  bluff  is  best,  because  of  the 
ease  of  blasting  and  loading  it.  The  value  of  limestone  for  macadam  road 
depends  upon  its  strength,  toughness,  resistance  to  wear  and  cementing 
power.  Strength  is  the  ability  to  stand  up  under  loads  without  crushing; 
toughness  in  contrast  to  brittleness  is  the  power  to  withstand  repeated  blows ; 
wear  resistance  denotes  the  amount  of  grinding  and  pounding  the  rock 
will  stand,  while  cementing  power  depends  upon  the  way  the  dust  produced 
by  crushing  and  wear  of  the  lime  particles  is  partially  dissolved  by  rain 
and  cemented  or  compacted  onto  and  between  the  rock  fragments.  Ce- 
menting power  is  of  extreme  importance,  for  even  though  the  other  quali- 
ties are  favorable,  if  the  dust  does  not  partially  dissolve,  then  precipitate 
between  the  pieces  and  cement  them  together,  the  macadam  will  have  little 
cohesion  and  will  "ravel"  along  the  edges,  while  the  surface  becomes  rough 
and  jagged  due  to  absence  of  dust  and  fine  material  which  are  needed  to 
make  a  surface  cushion. 

Both  the  Platteville  limestone  and  the  Galena  dolomite  make  satis- 
factory roads.  The  Platteville  is  stronger  and  harder,  and  has  a  higher 
wear  resistance  than  the  Galena,  but  the  latter  has  much  better  cementing 


GLASS    SAND  125 

power,  and  is  tougher.  Either  makes  a  better-than-average  macadam  road, 
but  under  the  present  high-speed  traffic,  the  greater  cementing  power  of  the 
Galena  makes  it  superior  to  the  Platteville.  Before  automobile  days,  the 
Platteville  made  more  desirable  road  metal,  but  the  severe  grinding  and 
high-wind  suction  of  modern  cars  remove  so  much  of  the  rock  dust  that 
greater  cementing  power  has  become  essential.  Probably  the  more  mas- 
sive beds  of  the  Shakopee  dolomite  could  make  good  roads,  but  the  more 
satisfactory   Platteville   outcrops   near  all   of   the    Shakopee   exposures. 

In  addition  to  quarries  supplying  merely  the  farm  on  which  they  are 
located,  30  quarries  have  been  opened  in  this  quadrangle  to  secure  build- 
ing stone,  commercial  lime  or  road  metal. 

Glass   Sand 

Glass  is  made  by  fusing  soda  or  lime  and  silica  together  and  cooling 
the  product  so  quickly  that  it  does  not  have  time  to  crystallize.  Partial 
crystallization  produces  a  cloudy,  non-transparent  material  which  is  worth- 
less. Other  substances  than  those  listed  are  sometimes  contained  in  the 
original  materials,  or  added  to  the  mixture  in  order  to  produce  special 
color,  brilliancy  or  strength.  Pure  white  quartz  sand,  free  from  iron  and 
clay,  is  the  most  desirable  source  of  silica.  Iron  makes  a  green  glass, 
such  as  is  common  in  low-grade  bottle  or  window  glass.  Alumina,  which 
is  an  essential  constituent  of  clay,  has  a  very  high  fusion  temperature 
and  almost  inevitably  produces  a  "milky"  glass.  Removing  the  clay  by 
washing  greatly  reduces  or  practically  eliminates  this  most  undesirable  con- 
stituent. 

Much  of  the  St.  Peter  sandstone  answers  all  requirements.  It  was 
thoroughly  cleaned  by  wind  and  water  before  it  was  deposited,  and  its 
total  impurities  are  normally  less  than  the  permissible  amount  of  iron  alone 
in  good  window-glass  sand.  The  St.  Peter  makes  a  glass  of  exceptionally 
high  quality,  and  is  the  basis  of  the  glass  sand  industry  both  in  this  area 
and  near  La  Salle. 

In  the  ground,  the  sand  has  little  value,  for  the  available  quantity  is 
unlimited,  and  the  selling  price  is  limited  to  the  cost  of  production,  plus  a 
moderate  profit.  Under  these  conditions,  the  success  or  failure  of  any 
glass-sand  plant  depends  upon  the  ability  of  the  management  to  finance 
the  undertaking  in  its  early  stages  and  to  market  the  sand  efficiently  and 
cheaply.  The  National  Silica  Company  is  operating  a  modern  plant  in  sec. 
8,  Oregon  Township  (fig.  19).  At  the  plant,  the  sand  is  quarried  by  drill- 
ing three-inch  holes  20  feet  from  the  face,  filling  them  with  explosive,  and 
breaking  off  the  face  of  the  quarry  (fig.  20).  The  sand  is  loaded  into 
quarry  cars  by  a  steam  shovel,  crushed  and  shipped  without  special  treat- 
ment if  merely  a  good  grade  of  sand  is  desired.     If  the  more  expensive, 


126 


DIXOX    QUADRANGLE 


Fig.   19.     Sand   crushing   and  washing   plant  of   the   National   Silica   Company, 

SE.  %  NE.  i/i  sec.  8.  T.  23  N..  R.  10  E.  Much  of  the  sandstone  face  has 

been  covered  by  soil  wash  from  above.  (Photograph  by  National  Silica 
Company.) 


;~^feto& 


Fig.   20.     View    in   sand   pit   of   the   National    Silica    Company,   Oregon,   SW.    y± 


strata  and  its  uniform  texture;  a  churn  drill  in  the  right  foreground  mak- 
ing blasting  holes  in  the  rock;  a  steam  shovel  loading  sand  for  the  plant; 
in  the  distance,  another  shovel  stripping  soil  and  vegetation.  (Photo- 
graph by  National  Silica  Company.) 


GLASS    SAND  127 

high-grade  sand  is  required,  after  being  crushed  to  separate  the  grains, 
it  is  washed  to  remove  clay  and  other  impurities.  The  company  is  able 
to  ship  this  sand  with  a  guarantee  of  not  over  one-half  per  cent  of  impuri- 
ties. 

The  following  analyses  made  by  Edward  Orton,  Jr.  for  the  National 
Silica  Company  are  published  through  the  courtesy  of  the  company,  and 
show  the  reported  character  of  the  sand  at  the  outcrop  and  of  the  product 
as  shipped  after  washing. 

Table  9. — Analyses    of   surface    and   washed   sand   from    quarry    of  the   National 

Silica    Company 

Surface  sand  Washed  sand 

Per  cent  Per  cent 

Si02 Silica 99.000  99.58 

A1203 Aluminum    oxide    .585  Trace 

Fe203 Iron    oxide .005  .23 

Ti02 Titanium    oxide Very  faint  Faint 

trace  trace 

CaO Lime     .235  None 

MgO Magnesia None  None 

K20 Potash     .016  ..... 

Na20 Soda    .039  

Loss   on   ignition .046  .05 


Total    99.926  99.86 

The  elimination  of  the  most  undesirable  impurity,  alumina,  is  clearly 
shown  by  the  analysis.  The  less  harmful  alkalies,  soda  and  potash,  and 
lime  have  also  been  eliminated.  The  iron  has  increased  as  a  result  of  the 
grinding  of  machinery  by  the  silica  and  possibly  because  the  washed  sand 
came  from  a  lower,  more  ferruginous  portion  of  the  deposit.  Experience 
has  shown  that  iron  increases  with  depth  and  has  even  reached  1.5  per 
cent.  This  is  not  because  different  strata  are  being  worked,  for  the  same 
bed  contains  more  iron  as  it  is  followed  back  under  cover.  In  most  cases 
of  weathering,  the  iron  content  increases  at  the  surface.  Here  the  iron  de- 
creases. Probably  the  abundant  vegetation  at  the  surface  helps  to  re- 
duce the  iron,  and  the  porosity  of  the  rock  favors  quick  transportation  of 
the  iron  downward  by  percolating  ground  water.  In  most  areas,  also,  iron 
is  concentrated  at  the  surface  by  removal  of  other  substances.  In  the 
absence  of  alkaline  carbonates,  silica  is  very  difficultly  soluble.  Since  silica 
is  practically  the  only  constituent  of  the  sand  besides  the  iron,  the  ferrugi- 
nous content  of  the  surface  is  not  appreciably  increased  by  weathering  pro- 
cesses. 

The  sand  is  used  not  only  for  ordinary  and  plate  glass,  bottles  and 
cheap   glassware,   but   also    for   the   finest   flint   and   cut   glass.      It   is   also 


128  DIXON    QUADRANGLE 

purchased  in  great  quantity  for  use  in  the  sand-blast  process  of  cutting 
and  frosting  glass,  and  as  an  abrasive,  for  sawing  stone,  polishing  and 
grinding.  Much  sand  is  also  crushed  here  to  pass  a  140-mesh  screen  and 
sold  under  the  trade  name  of  "flint."  True  flint  is  not  a  crystalline  quartz 
like  this,  but  is  a  form  of  chert.  However,  powdered  until  no  piece  is 
more  than  1/250  inch  in  diameter,  this  rock  flour  is  said  to  serve  all  pur- 
poses of  flint  in  making  chinaware.  In  addition  to  these  uses,  because  of 
its  purity  large  sales  are  made  for  chemical  purposes,  particularly  for 
making  sodium  silicate  or,  as  it  is  commonly  known,  water  glass. 

Supplies  of  this  sand  are  practically  unlimited  since  it  is  available 
at  the  surface  over  all  the  area  indicated  on  the  geologic  map.  The  sand 
averages  at  least  50  feet  in  thickness,  and  in  some  places  reaches  over  150 
feet.  A  thickness  of  50  feet  would  produce  50,000,000  cubic  yards  or 
110,000,000  tons  per  square  mile. 

Sand  and  Gravel 

Building  sand  and  gravel  are  found  in  this  area  primarily  as  a  result 
of  glaciation  and  do  not  bear  any  necessary  relation  to  the  formations  un- 
derlying the  valleys  in  which  they  occur.  In  regions  of  stream  erosion,  un- 
interrupted by  glaciation,  sand  and  gravel  accumulate  in  valleys  where 
erosion  is  rapid,  or  where  certain  materials  successfully  resist  weathering. 

In  this  area,  the  commercial  sources  of  these  building  materials  are 
the  Rock  and  Kyte  River  valley  trains  and  the  Grand  Detour  esker.  Glacial 
erosion  was  rapid  and  deep,  with  no  opportunity  for  chemical  weather- 
ing. Accordingly,  the  glacial  gravels  consist  of  both  hard  and  soft  rock 
fragments.  Limestone  predominates  because  it  is  the  common  surface  rock 
in  the  region  and  most  glacial  drift  has  had  a  local  origin.  Sandstone 
pebbles  are  not  common  in  the  gravel,  for  most  of  the  neighboring  sand- 
stones are  poorly  cemented.  Rolling  by  the  streams  disintegrated  much 
of  the  softer  local  material,  and  the  swiftly  running  water  washed  away 
the  finer  constituents.  Igneous  and  hard  metamorphic  rocks  have  there- 
fore contributed  a  much  larger  percentage  to  the  gravel  than  to  the  till. 

The  long  transportation  of  the  Late  Wisconsin  valley  train  material 
thoroughly  washed  the  sand.  Most  of  the  gravel  was  not  carried  to  this 
quadrangle.  Estimates  of  the  material  over  one-fourth  of  an  inch  in 
diameter  commonly  vary  from  less  than  5  per  cent  to  10  or  12  per  cent. 
Much  of  the  sand  is  sharp  and  angular ;  but  readily  recognizable,  wind- 
blown sand  grains  from  the  St.  Peter  and  Croixan  formations  are  com- 
mon.    All  of  the  valley-train  gravels  are  fairly  well  rounded. 

The  supply  of  sand  and  gravel  is  practically  inexhaustible.  Pits  may 
be  opened  at  any  point  in  the  valley  train  and  a  good  quality  and  abundant 
quantity  of  sand  and  fine  gravel  will  be  obtained  except  where  bed   rock 


SAND   AND   GRAVEL — POTASH  129 

is  close  to  the  surface.  Many  terraces  of  this  valley  train  stand  over  30 
feet  above  present  water  level  in  Rock  River,  and  by  dredging,  sand  and 
gravel  could  be  taken  from  a  depth  of  60  feet  beneath  the  present  river 
level. 

The  distribution  of  the  upland  gravels  of  the  Grand  Detour  esker  is 
indicated  on  Plate  I.  This  material  was  water-transported  for  a  very 
short  distance  and  is  not  so  well  washed  and  sorted  as  the  valley-train 
deposits.  The  esker  deposits  carry  a  much  higher  percentage  of  gravel, 
at  least  40  per  cent  of  the  material  being  over  a  quarter  of  an  inch  in 
diameter. 

The  beautifully  rounded  St.  Peter  and  "New  Richmond"  sands  are 
not  satisfactory  for  building  purposes.  A  sharp,  angular  sand  is  desired, 
first  because  sharp  grains  cannot  be  rotated  or  twisted  in  the  mortar  or 
cement  so  easily,  and  second,  lime  or  cement  must  be  added  to  fill  all  the 
spaces  between  the  sand  grains.  Otherwise  a  porous,  unsubstantial  struc- 
ture results.  There  is  more  space  between  rounded  grains  of  uniform 
size  than  between  angular  ones,  and  the  cement  or  lime  consumption  is 
therefore  higher.  The  sandstones  would  be  more  expensive  to  quarry 
than  the  valley-train  and  esker  sands. 

Potash 

Three  elements  are  required  in  great  amounts  annually  for  fertilizers 
in  this  country ;  namely,  phosphorus,  nitrogen  and  potassium.  The  deposits 
of  Florida  are  sufficient  for  the  present  demand  for  phosphorus  in  the  form 
of  phosphates,  and  tremendous  reserves  in  Idaho,  Utah  and  adjoining  states 
promise  a  supply  for  at  least  6,000  years  for  all  the  world  at  the  present 
rate  of  consumption.  Nitrates  come  in  abundance  only  from  Chile.  The 
farmer  can  supply  his  own  nitrates,  aside  from  those  contained  in  manure 
and  other  organic  material,  largely  by  growing  various  legumes,  such  as 
clover,  alfalfa,  peas,  and  beans,  which  take  nitrogen  from  the  air  and  store 
it  in  the  ground  in  useful  form.  In  case  of  urgent  need,  nitrates  may  be 
manufactured  from  the  air  by  use  of  electricity,  and  the  government  built 
the  great  Muscle  Shoals,  Alabama,  plant  to  provide  nitrates  for  military 
purposes. 

In  potash,  the  country  is  not  self-sufficient.  In  spite  of  years  of  re- 
search and  effort  to  secure  an  adequate  supply  from  various  sources,  during 
the  World  War  and  under  the  stimulus  of  four-fold  increase  in  price,  only 
40  per  cent  of  the  normal  potash  consumption  was  produced  in  this  country. 
Germany  had  a  virtual  monopoly  on  the  potash  of  the  world  before  the 
war:  with  the  return  of  Alsace  to  France,  Germany  lost  the  lesser  of  the 
two  deposits  which  she  had,  and  France  is  now  a  competitor  for  the  world 


130 


DIXON    QUADRANGLE 


trade.  The  two  largest  producing  areas  in  the  United  States  are  the  alka- 
line lakes  of  northwestern  Nebraska  and  the  salt  marshes  of  southern  Cali- 
fornia. Neither  of  these  has  a  large  reserve,  and  the  1919  rate  of  produc- 
tion would  exhaust  them  both  within  20  years.  Other  sources  of  potash 
are  therefore  of  great  importance,  even  though  they  may  be  reserves  for 
the  future,  rather  than  commercial  possibilities  at  present. 

The  Glenwood  shale  carries  an  unusual  amount  of  potash,  apparently 
in  the  form  of  glauconite.  The  following  analyses  were  made  by  J.  M. 
Lindgren  of  the  University  of  Illinois  of  samples  taken  by  the  writer  in  the 
Dixon  quadrangle. 

Table  10. — Potash  content  of  samples  from  deposits  in  the  Dixon  quadrangle 


Sample 
number 

Location 

Potash  content 

Part  of  section 

Section 

Township 

1 

1000  feet  E.  and  500  feet  N.  of 
S W    corner    

15 
23 
34 
11 

Dixon 

Nashua 

China 

Grand  Detour 

Per  cent 
5.83 

4 

2000  feet  N.  of  SW.  corner  on 
west  line   

5.79 

7 

500  feet  E.  and  1600  feet  N.  of 
SW.   corner    

5.83 

8 

1000   feet  E.   and'  3200   feet  N. 
of  SW.   corner 

.22 

Sample  No.  1  covers  5  feet  of  Glenwood  shale  outcropping  in  a  ravine. 
This  is  practically  the  complete  section  of  the  Glenwood  at  this  point.  The 
top  6  to  10  inches  was  covered  by  slumping  rock.  The  sample  was  taken 
by  channeling  three  inches  wide,  one  inch  deep  across  outcrop,  and  quarter- 
ing down.  Sample  No.  4  represents  3^  feet  of  Glenwood  shale  exposed 
in  the  bottom  of  a  small  quarry.  The  sample  was  taken  by  channeling,  as 
before.  The  total  thickness  of  Glenwood  here  is  about  six  feet,  as  esti- 
mated by  leveling  between  exposures.  Sample  No.  7  is  not  from  the  Glen- 
wood, but  from  the  green  shale  which  underlies  the  St.  Peter  in  Franklin 
Creek  valley.  It  was  taken  by  channeling  and  quartering  across  30  inches 
of  the  shale.  The  top  and  bottom  are  both  exposed.  No.  8  is  not  a  sample, 
but  simply  a  piece  of  the  exposure  at  Green  Rock  of  the  most  prominent 
green  glauconite  bed  in  the  upper  St.  Peter.  As  noted  in  the  description 
of  the  St.  Peter,  the  green  clay  is  a  coating  and  matrix  embedding  quartz 
grains  identical  with  those  making  up  the  remainder  of  the  sand.  In  the 
hand  specimen,  and  under  the  microscope,  it  appears  to  be  identical  with 
the  typical  Glenwood  shale  which  lies  10  feet  higher.  Under  the  micro- 
scope, this  glauconite  was  estimated  as  5  per  cent  of  the  rock:  since  the 


PETROLEUM  131 

potash  is  confined  to  the  clay,  there  must  be  about  4  per  cent  potash  in  the 
clay,  indicating  that  it  is  essentially  similar  to  the  Glenwood  above. 

The  Glenwood  was  found  wherever  the  top  of  the  St.  Peter  was  ex- 
posed, on  the  west  flank  of  the  La  Salle  anticline.  It  is  difficult  to  meas- 
ure the  shale  thickness  because  the  overlying  Platteville  slumps  badly  on 
this  slippery  "soapstone",  as  it  is  locally  called.  Thicknesses  as  little  as  2 
feet  were  measured,  but  where  the  relations  seemed  undisturbed  by  sliding, 
the  amount  varies  from  3  to  7  feet.  On  the  crest  of  the  anticline  and  at 
the  only  good  exposure  on  the  Prairie  View  syncline,  the  Glenwood  shale  is 
commonly  thin,  and  locally  is  missing  entirely.  In  important  quantities  it 
can  be  looked  for  only  west  of  the  anticline  in  the  Dixon  area.  The  aver- 
age shale,  as  determined  from  78  analyses  by  Clarke2,  carries  3.25  per  cent 
potash,  so  that  the  Glenwood  contains  nearly  180  per  cent  of  the  normal 
amount.  Under  present  costs  and  methods,  it  is  impracticable  to  work  this 
material  for  its  potash  alone.  It  is  probable  that  the  potash  may  be  re- 
covered as  a  cement  plant  by-product,  and  be  of  value  in  the  future.  It  is 
hoped  that  the  Glenwood  may  be  studied  to  the  north  and  west  where  it 
is  thicker  to  see  whether  its  potash  content  is  as  favorable  there,  where  min- 
ing it  would  be  much  less  expensive. 

Petroleum 

The  bright,  iridescent  scum  of  limonite  (iron  oxide),  commonly  seen 
on  the  surface  of  swamps,  has  frequently  been  regarded  as  petroleum. 
Much  time  and  energy  have  been  wasted,  as  in  the  case  of  two  or  more  wells 
drilled  near  Honey  Creek,  in  search  of  the  oil  that  was  supposedly  indicated 
by  this  iron  oxide  scum.  Two  very  simple  tests  will  quickly  tell  whether 
petroleum  is  present.  Oil  floating  on  water  makes  a  film  which  will  unite 
again  if  broken  by  gently  stirring  the  surface,  whereas  limonite  will  break 
into  sharp-edged  fragments  which  do  not  merge,  but  may  overlap  if  one  is 
carried  over  the  other  by  splashing  water  or  a  sudden  wave.  The  other  test 
is  to  see  if  the  substance  will  burn.  Petroleum  may  not  flash  to  a  match, 
like  gasoline,  but  any  petroleum  found  in  the  Mississippi  valley  will  burn 
if  a  flame  is  touched  to  it. 

Petroleum  may  be  collected  by  skimming,  or  if  there  is  a  very  small 
amount,  it  may  be  skimmed  into  a  bottle  having  a  large  body,  but  very 
small  neck.  The  petroleum  from  a  large  quantity  of  water  is  thus  collected 
in  the  small  neck,  and  may  be  removed  and  tested.  Limonite  will  not  col- 
lect in  this  way.  The  smell  and  taste  of  the  water  are  often  appealed  to, 
but  few  people  know  the  taste  of  stagnant  water,  and  think  it  tastes  as  pe- 
troleum probably  does.     Testing  by  breaking  the  surface  and  by  flame  will 

2  Clarke,  P.  W.,  The  data  of  geochemistry:  U.  S.  Geol.  Survey  Bull.   695,  p.   29,   1920. 


132  DIXON    QUADRANGLE 

save  the  expense,  trouble,   and   disappointment  of   having  an  examination 
made  in  the  great  majority  of  supposed  petroleum  showings. 

There  is  little  possibility  that  petroleum  will  be  found  in  this  area.  In 
the  first  place,  petroleum  production  is  conditional  upon  the  presence  of 
favorable  structures  covered  by  impervious  strata  which  will  confine  the 
oil  and  gas  until  man  reaches  them  with  the  drill.  The  only  desirably  shaped 
structures  in  this  area  have  St.  Peter  sandstone  outcropping,  and  no  oil  has 
been  produced  from  rocks  as  old  as  those  underlying  the  St.  Peter. 

Secondly,  as  already  stated,  oil  accumulation  demands  a  trap  which  will 
retain  oil  and  gas.  An  impervious  rock,  usually  a  shale,  must  cover  the 
reservoir,  in  order  to  make  this  trap.  The  only  continuous  shales  of  the 
area  are  those  in  the  Prairie  du  Chien,  and  the  upper  part  of  the  Croixan 
formations.  If  they  were  capable  of  confining  petroleum,  the  original  salt 
water  of  the  ocean  could  not  have  escaped  from  beneath  them.  All  the  deep 
wells  in  the  area  penetrate  these  shales  and  find  below  them  an  adequate 
supply  of  fresh  water  for  Dixon,  Amboy  and  Oregon.  Such  quantities  of 
fresh  water  indicate  that  water  is  moving  through  the  underlying  sands  with 
ease,  and  if  oil  has  ever  existed  here,  it  has  long  since  escaped  and  disap- 
peared. 

Natural  Gas 

Gas  may  be  found  in  small  quantities,  as  it  is  now  produced  from  the 
Green  River  valley  to  the  south  and  near  Chana,  adjacent  to  the  northeast 
corner  of  the  quadrangle.  This  gas  is  not  associated  with  oil,  but  probably 
comes  from  the  decay  of  plant  matter  buried  by  glacial  deposits.  Such 
gas  also  forms  in  wood-curbed  wells  which  are  tightly  closed  in,  and  in 
abandoned  mine  workings,  where  much  timber  is  left  in  the  ground.  These 
gas  pockets  will  have  small  production  and  probably  a  rather  short  life. 
They  cannot  be  predicted  from  surface  indications,  except  that  the  chances 
are  better  for  them  where  a  preglacial  channel  has  been  buried  by  drift. 
In  such  a  place,  much  plant  matter  may  have  been  covered,  and  may  since 
have  generated  considerable  gas. 

The  chances  for  a  large  gas  field  are  the  same  as  those  for  oil,  since  oil 
and  gas  are  formed  and  collected  under  identical  conditions.  There  is  no 
hope  for  gas  development  on  a  commercial  scale  in  this  area. 

Ore  Minerals 

The  term  ore  minerals  is  used,  because  there  are  no  ores,  nor  prospect 
of  any  within  this  area.  An  ore  is  a  rock  or  aggregation  of  minerals  from 
which  one  or  more  metals  may  be  extracted  at  a  profit.  An  ore  mineral  is 
a  mineral  which  in  sufficient  concentration  constitutes  an  ore. 


NATURAL   GAS ORE    MINERALS  133 


SULPHIDES 


In  the  Platteville  limestone,  three  sulphides  are  found  which  in  suffi- 
cient quantity  would  be  valuable.  They  are  the  sulphides  of  lead,  zinc  and 
iron,  known  technically  as  galena,  sphalerite  (zinc  blende,  rosin  or  black 
jack,  depending  on  its  color)  and  pyrite  (pyrites,  fool's  gold,  sulphur  or 
iron).  In  the  northwestern  part  of  the  State,  all  of  these  are  found  in  suffi- 
cient quantity  to  be  ores,  both  in  the  Galena  dolomite  and  to  a  slight  extent 
in  the  Platteville  limestone.  In  this  quadrangle,  they  have  been  found  only 
in  the  Platteville  and  Glenwood  formations  and  only  in  very  small  amounts. 
Galena  occurs  in  steel-gray  cubes  which  are  easily  scratched  wTith  a  knife, 
and  breaks  conspicuously  along  planes  parallel  to  the  sides  of  the  cube ;  the 
mineral  is  very  heavy ;  its  powder  is  black,  and  it  will  fuse  to  a  lead  globule 
on  a  red  hot  stove,  with  the  typical  smell  of  burning  sulphur.  The  sphalerite 
looks  like  masses  of  yellow,  red-brown  or  black  rosin.  Scratching  with  a 
knife  produces  a  yellow  or  buff  powder.  Sphalerite  will  not  melt  nor  burn 
at  ordinary  temperatures,  and  is  only  iy2  times  as  heavy  as  limestone. 
Pyrite  is  best  described  by  its  popular  name,  fool's  gold,  for  it  is  more  often 
mistaken  for  gold  than  any  other  mineral.  Pyrite  is  usually  found  in  per- 
fect cubes,  which  do  not  break  with  plane  surfaces.  It  is  brassy  to  golden 
yellow  when  fresh,  but  turns  brown  and  eventually  becomes  iron  rust  upon 
long  weathering.  It  is  too  hard  to  scratch  with  a  knife,  has  a  green-black 
powder,  is  twice  as  heavy  as  limestone,  ignites  with  difficulty,  produces  the 
typical  odor  of  burning  sulphur  on  ignition,  and  leaves  a  magnetic  residue. 

As  already  stated,  none  of  these  has  been  found  in  such  amount  as  to 
give  any  hope  that  valuable  quantities  occur  in  this  quadrangle.  The 
amounts  are  extremely  minute  and  similar  small  quantities  are  often  found 
in  limestones.  In  1922,  the  lead  and  zinc  ores  sold  for  about  three  cents 
per  pound  and  pyrite  was  worth  about  $6.00  per  ton.  These  prices  are 
cited,  not  because  people  may  find  ore  deposits,  but  to  prevent  the  fre- 
quent arousing  of  false  hopes  based  on  exaggerated  ideas  of  the  value  of 
these  minerals. 

All  of  these  sulphides  appear  in  the  casts  of  gastropod  shells  in  the 
limestone,  none  of  the  specimens  being  found  in  veins.  Their  uniform 
occurrence,  coating  the  interior  casts,  shows  very  clearly  that  iron,  lead  and 
zinc  were  present  in  the  ocean  of  that  time  and  were  reduced  and  precipi- 
tated by  organic  matter.  No  reason  is  known  for  their  appearance  in 
gastropod  shells  alone,  but  possibly  these  animals  contained  much  sulphur, 
and  on  decaying,  the  sulphur  formed  hydrogen  sulphide  and  precipitated 
the  metallic  sulphides.  If  the  sulphides  were  introduced  at  a  hter  time  they 
would  have  been  found  in  veins  or  fissures  in  the  rock,  rather  than  being 
confined  to  the  one  type  of  occurrence  noted. 


134  DIXON    QUADRANGLE 

Pyrite  is  very  common  in  shales  and  clays.  The  only  mine  ever 
opened  in  this  quadrangle  was  a  drift  in  the  Glenwood  shale  where  pyrite 
led  the  prospector  to  expect  gold.  This  prospect  was  opened  on  the  south 
side  of  sec.  22,  Dixon  Township,  on  the  outcrop  of  the  Glenwood  shale. 
Small  lumps  of  concretionary  pyrite  scattered  through  the  shale  attracted 
the  attention  of  Simon  Smith,  who  worked  here  for  several  months  in  1907 . 
His  equipment  consisted  of  a  small  car  and  some  trackage,  a  pick  and  a 
shovel.  Xo  blasting  was  done  :  since  he  was  working  up  dip.  the  water 
drained  out.  The  workings  consisted  of  a  straight  drift  extending-  into 
the  hillside  from  150  to  300  feet,  according  to  various  reports.  The  caved 
ground  at  present  proves  only  that  he  went  at  least  50  feet,  and  there  is 
no  way  to  determine  how  much  farther  he  proceeded,  since  he  never  per- 
mitted any  one  to  enter  the  prospect.  The  drift  was  four  feet  wide  and 
live  feet  high,  abundantly  timbered  with  3-inch  posts,  caps  and  sills.  Va- 
rious reports  of  gold,  silver,  lead  and  platinum  production  are  current,  but 
no  one  interviewed  ever  saw  these  metals,  except  the  lead.  Mr.  Smith 
finally  abandoned  the  prospect  and  left  the  region.  The  dump  shows  a 
quantity  of  Glenwood  shale,  with  concretionary  masses  of  pyrite  and  an 
occasional  cube  of  galena.  No  trace  of  the  other  metals  was  found,  and 
there  is  no   reason  to  think  they  ever  were  present. 

LIMONITB 

Iron  ore  is  frequently  reported  by  people  engaged  in  drainage  opera- 
tions. Masses  of  limonite  I  hydrated  iron  oxide,  or  iron  rust  I  are  com- 
monly found  in  the  muck  of  old  swamps  and  marshes.  Limonite  is  an 
iron  ore  mineral  and  would  be  valuable  if  found  in  large  quantity.  Water 
circulating  through  the  till  may  take  iron  into  solution  and  carry  it  until 
it  comes  in  contact  with  air.  Then  the  iron  is  precipitated  as  an  iri- 
descent, oily-appearing  him  which  floats  on  the  water,  but  eventually  set- 
tles to  the  bottom  and  forms  the  lumps  of  limonite  referred  to  above.  Such 
limonite  films,  frequently  mistaken  for  petroleum,  are  commonly  found 
on  stagnant  water  in  the  glaciated  regions,  and  the  small  lumps  are  found 
in  the  deposits  of  plant  matter  that  accumulate  beneath  these  swamps. 
It  is  natural,  therefore,  that  the}"  should  be  found  most  commonly  in 
drainage  operations,  where  a  poorly  drained  depression  tilled  with  vege- 
tation is  being  prepared  for  cultivation.  This  iron  ore  is  worth  about  $2.00 
per  ton,  so  that  it  is  obvious  large  quantities  would  have  to  be  available 
to  make  a  commercial  deposit.  No  iron  mines  in  this  country  are  work- 
ing in  any  such  ore.  and  it  is  highly  improbable  that  such  ore  exists  here.  It 
would  have  to  be  at  least  1()  feet  thick  over  a  large  area  to  have  any  value. 
There  is  no  source  for  such  a  quantity  of  iron,  nor  is  any  present  or  ex- 
tinct marsh   of   sufficient   size  known. 


ORE    MINERALS  135 

COPPER  AND  GOLD 

Fragments  of  native  copper  transported  from  Canada,  or  doubtfully, 
northern  Michigan,  have  been  found  in  the  drift.  Several  people  report 
having  seen  gold  panned  from  the  gravel  in  Rock  River.  No  one  is  said 
ever  to  have  made  a  living  in  this  way,  nor  is  any  one  likely  to.  Gold  is 
known  in  the  drift,  but  always  in  infinitesimal  quantities,  and  no  com- 
mercial production  from  the  drift  is  known.  The  gold  in  this  quadrangle, 
like  the  glacial  erratics,  came  from  Canada  and  is  so  mixed  with  tremen- 
dous quantities  of  other  material  that  it  cannot  be  profitably  obtained. 


INDEX 


A 

PAGE 

Acknowledgments    12 

Alluvium,  flood-plain   78 

Amboy,   city  well   of 34,  35 

Amplexopora  sp 64 

Area  of  quadrangle 11 

Artesian  wells   117-119 

Arthropora  simplex  Ulrich 59 

B 

Backwater  deposits    78 

Batostoma  cf.   magnopera  Ulrich  59 

Batostoma  winchelli   Ulrich 59 

Bellerophon   troosti   D'Orbigny. ..  64 

Bibliography   11-12 

Bucania   nashvillensis    Ulrich....  64 

Buff  limestone,  description  of...  54 

section   of    56 

C 

Cady,  G.  H.,   cooperation  of 12 

Cambrian  period,  deposition  dur- 
ing           81 

life   in   80 

Cambrian  system,  description  of. 36-39 
Garabocrinus     cf.     radiatus    Bil- 
lings           59 

Cement  materials    119-122 

Cenozoic  group    66-79 

Chamberlain      Creek,      preglacial 

course  of  99 

Clastics,  formation  of 24 

Clathrospira  subconica  Hall....  59 
Clear  Creek  basin,  dolomite  in..  83 
Clear     Creek,     preglacial     course 

of    99 

Climate   13 

Columnaria   halli  Nicholson 59,89 

Communication    18 

Consolidation  of  sediments 27 

Constellaria  varia  Ulrich 59 

Continental  glacier,   definition  of       23 

Copper  in  the  drift 135 

Correlation  of  formations 28-30 

Crania  trentonensis  Hall 59 


PAGE 

Cross-sections    illustrating    pene- 
plain  surface    91 

Croixan  series    36-39 

water  wells   in 117-119 

Cuestas,  formation  of 92 

Culture    18 

Cyrtoceras   sp 59 

Gyrtodonta     obliqua     Meek     and 

Worthen    59 

Gryptozoon    83 

Gryptozoon     minnesotense     Win- 

chell    47 


Dalm.anella  testudinaria  Dalman  59 
Daysville,   sand   dunes   southwest 

of   102 

Dekayella  praenuntia  Ulrich....  59 
Demangeon,    Albert,    explanation 
of  unequal  erosion  in  valley 

sides    103 

Devils  Backbone,  anticline  south- 
eastward   from 109 

elevation  of 13 

Dinorthis  pectinella  Emmons. ...  59 

Dixon,  deep  well  near 36 

population   of    18 

Dixon     Epileptic     Colony,     wells 

of    35,  36,  38,45,50,  117 

Dixon    State    Hospital,    analysis 

of  water  from  well  of 116 

Dixon   Water   Company,   wells  of 

34,  35,  36,  37,  50-51,117 

Dolomite,  formation  of 24-25 

Drainage    16 

Drainage    development,    post-Illi- 

noian    98-101 

Drift,   definition   of 27 

Dunes,    definition   of 22 

formation    of    25 


Economic  geology    112-135 

Elevation    of  area 13 


137 


13S 


INDEX— Continued 


PAGE 

Encrinurus    vannulus   Clarke....  59 

Endoceras  proteiforme  Hall 59 

Eolian   deposits    25 

Eridotrypa  aedilis  Eichwald 59 

Eridotrypa   aedilis    minor   Ulrick  59 

Erosion,   definition   of 22-23 

Escharopora   subrecta   Ulricli....  59 

Eskers.   definition  of 27 

Eurychilina   reticulata  Ulrick....  59 

F 

Faults  in  Dixon   area Ill 

Field   work    12 

Flood-plains     16 

Fossils,    definition    of 29 

in    Galena    dolomite 64 

in  Platteville   limestone 59-60 

in  Skakopee  member 17 

Franklin  Creek  section 45 

Fusispira     angusta     Ulrick     and 

Scofield     64 

G 

Galena    dolomite,    areal    distribu- 
tion  of    64 

correlation  of   65 

description  of  61-62 

dolomitization   of    90 

fossils   from    64 

paleontologic  ckaracter  of 64 

quarries   in    123 

tkickness   of    62-63 

Galena  in  Platteville  limestone..  133 
Galena  stage,  conditions  during.  .S9-90 
Galloway,  J.  J.,  assistance  of .  .  .  .  12 
Geologic  column  for  quadrangle  32 
Geologic    formations,    table    of...       33 

Geologic  time  table 28 

Glacial  deposits   26-27 

Glacial    invasions    of    the    United 

States    94 

Glass  rock  of  the  Blue  limestone, 

description  of  54 

section    of    57 

Glass    sand    125-128 

Glenwood    shale,    conditions    dur- 
ing   formation    of 86-87 

correlation  of  53 

description    of    52 

extent  of    53 


PAGE 

source   of  potash 130-131 

thickness  of    52 

Gold   in   tke   drift 135 

Gonioceras  oceidentale  Hall 59 

Grand  Detour,  a  summer  resort..       16 

sand  dunes  nortk  of 102 

Grand    Detour    esker 73-74 

age   of   96 

evidences    of    direction    of    ice 

movement   in    95 

source  of  commercial  sand  and 

gravel    128 

Green  Rock,  exposure  of  St.  Peter 

sandstone   at   49,  51 

Ground  water,  definition  of 28 

H 

Heoertella    sp 64 

Hemipliragma   irrasum  Ulrick...  59 
Holopea  excelsa  Ulrich  and  Sco- 
field      64 

Homotnjpa   minnesotensis  Ulrich  59 

Homotrypa   similis   Foord 64 

Homotrypa    sp 64 

Honey   Creek,    well   near 36 

Hormotoma   gracilis  Hall 64 

Hormotoma   major  Hall 64 

Hormotoma   sp 47 

Human      activities,      erosional 

effects  of    104-106 


Illaenus  americanus  Billings....  64 
Illaenus  punctatus  Raymond....  59 
Illinoian  ice-skeet,  kistory  of.. ..95-96 

Illinoian  till    67-73 

Industry    18 

Iowan    (?)    till 67-73 

Iron    ore    134 

Iscliaditcs   ioicensis   Owen 64 

K 

Keweenawan   sandstone    34-36 

Kyte  River,  preglacial  course  of.       99 

sand    and    gravel    from    valley 
train   of    128 

valley  train  in  valley  of 76 

L 

Lake  deposits  26 

Land   division,   method   of 20-21 


INDEX — Continued 


139 


PAGE 

La   Salle   anticline 

86,  87,  89,  107,  109,  110 

Late  Wisconsin  valley  train,  sec- 
tion  of    77 

Leighton,  M.  M.,  cooperation  of .  .       12 

Leperditia  fabulites  Conrad 59 

Le'ptaena      charlottae      Winchell 

and    Schuchert    59 

Leverett,    Frank,    views    on    pre- 

glacial   drainage    99-100 

Lichenaria    typa    Winchell     and 

Schuchert     59 

Limestone,    formation    of 24 

Limestone    and    limestone    prod- 
ucts     122-125 

Limonite,  occurrence  of   134 

Lingula   elderi   Whitfield 59 

Lingulepis  acuminata  Conrad....  47 
Liospira  americanus  Billings ...  64 
Liospira  obtusa  Ulrich   and   Sco- 

field    59 

Liospira  progne   Billings 59 

Liospira   sp 47 

Liospira  vitruvia  Billings 59 

Location  of  area 11 

Loess,  age  of 75-76 

definition  of    25 

description    of    74-76 

for  use   in  manufacture   of  ce- 
ment         120 

Lophospira   augustina  Billings...       64 

Lophospira   bicincta  Hall 59,64 

LopTiospira  obliqua  Ulrich 59,  64 

Lowell     Park     member,     descrip- 
tion  of    54 

section   of    57,  58 

M 

Maquoketa  shales   65 

Marine  deposits,  stratification  of       23 
Martin,     Lawrence,     views     on 
origin     of     land     forms     in 
southern    Wisconsin    and 

northern    Illinois    91-92 

Middle    Ordovician    series 48-65 

Moraines,  definition  of 26 

Muck  deposits    78-79 

N 
National   Silica   Company,   analy- 
ses of  sand  from  quarry  of..     127 


PAGE 

plant  and  sand  pit  of 125-126 

Natural   gas    132 

"New   Richmond"    sandstone, 

areal  distribution  of 42 

correlation  of   42-43 

description  of 40-42 

"New    Richmond"     stage,     condi- 
tions   during   81-82 

Niagaran  limestone    65 

O 

Oneota   dolomite,    areal    distribu- 
tion  of    40 

conditions     under     which     de- 
posited           81 

correlation  of  40 

description   of    39-40 

Ophileta  sp 47 

Ophiletina    sublaxa    Ulrich     and 

Scofield     59 

Ordovician  system    36-65 

Oregon  Basin,  structure  of 110 

Ore   minerals    132-135 

Orthis  tricenaria  Conrad 59 

Orthoceras  cf.  sociale  Hall 59 

Orthoceras    sp 59 

P 

Pachydictya  actua  Hall 59 

Paleozoic  group,  description  of.. 36-66 

Paleozoic   record,   later 90 

Peat  deposits    7S-79 

Peneplains    90-93 

Pennsylvania    Corners,    bifurcat- 
ed syncline  near 109 

Pennsylvania    Corners-Grand    De- 
tour   syncline    109 

Peorian    interglacial   epoch 96-97 

Petroleum    131-132 

Phragmolithcs   fimbriatus    Ulrich 

and    Scofield    59 

Physiographic  cycle    30-31 

Physiographic  province  13 

Pianodcma  subaequata  Conrad..  59 
Pine  Creek,  preglacial  course  of.  99 
Platteville   limestone,   correlation 

of    60-61 

description    of    53-55 

distribution    of   5S 

division    of    53-54 


140 


INDEX—  Continued 


PAGE 

fossils   from    59-60 

ore    minerals    in 133 

paleontologic  character  of 58 

quarries  in    122-123 

sections    of    56,  57,  58 

thickness  of    55 

topographic  expression  of 55 

uses  of    124-125 

Platteville  stage,  conditions  dur- 
ing     87-89 

Plectambonites  sericeus   Sowerby       59 

Pleistocene   period    94-101 

Population    18 

Potash     129-131 

Prairie  du  Chien  series 39-48 

division   of    39 

Prairieside    School,    sand    dunes 

north   of   102 

Prairie  View  syncline 110,  111 

Pre-Cambrian  eras,  history  of...       80 

Pre-Cambrian  rocks   34-36 

Pre-Illinoian    glaciation,    evidenc- 
es  of    94-95 

Pre-Illinoian   deposits    66 

Pyrite,  in  Glenwood  shale 134 

in  Platteville  limestone 133 

R 

Rafinesqui?ia  alternata  Emmons. 59,  64 
Rafinesquina  minnesozensis  N.  H. 

Winchell    59,64 

Recent  history  101-106 

Recent  sediments    78-79 

Recevtaculites    oiveni   Hall 63,64 

Relief  of  area 13 

Rhinidictya   exigua   Ulrich 59 

Rhinidictya  grandis  Ulrich 59 

Rhinidictya   mutabilis   Ulrich....       59 

Rhinidictya  sp 64 

Rhinidictya   trentonensis  Ulrich.       60 
Rhynchotrema  increbescens  Hall       64 

Rocks,   classification   of 21-22 

Rock  River,  dissection  by 14 

drainage    changes    in 99-101 

dunes  along    79,  102 

effect  of  glacier  on 97-98 

gagings  of  17 

Platteville-Galena     contact     at 
dam   of    62 


PAGE 

sand    and    gravel    from    valley 

train   of    128 

valley  of    16 

Run-off,   definition   of 28 

S 

St.  Peter  sandstone,  areal  distri- 
bution of   50 

conditions  of  deposition  of.... 85-86 

correlation   of   51-52 

description    of 48-50 

elevations  of  top  of 108 

paleontologic   character  of 51 

thickness  of    50 

topographic   expression   of 50 

uses  of   125 

water  wells  in 116-117 

Salpingostoma  buelli  Whitfield.  .       60 

Sand  analyses    127 

Sand  and  gravel 128-129 

Sand  dunes  79 

Sandusky    Cement    Company, 

plant  and  quarry  of 120,121 

Sangamon  interglacial  epoch....       96 

Savanna-Sabula   anticline 107, 110 

Scenidium  anthonense  Sardeson.       60 
Scolithus  minnesotensis   Hall....       51 

Scolithus  sp 60 

Sevenmile    Branch,    preglacial 

course  of   99 

Shakopee    dolomite,    areal    distri- 
bution   of   45 

conditions  under  which  formed 

82-85 

correlation  of  47-48 

description    of    43-44 

fossils   from    47 

paleontologic  character  of 46 

sections  of 45,  46 

thickness  of   45 

Shakopee  sediments,  deformation 

of   83-84 

Sink  holes  in  quadrangle 102 

Sinuitcs    canccllatus    Hall 64 

Sinuitcs     canccllatus     trentonen- 
sis Ulrich  and  Scofield 64 

Sphalerite     in     Platteville     lime- 
stone          133 

Springs   113-114 

Spyroceras  bilincatum  Hall 60 


INDEX—  Concluded 


141 


PAGE 

Stream  deposits  25-26 

Streptelasma   corniculum  Hall...  60,  64 
Streptelasma   projundum   Conrad 

(Owen)     60 

Strophomena    emaciata   Winchell 

and  Schuchert   60 

Strophomena   incurvata    Shepard       60 
Strophomena    scofieldi    Winchell 

and   Schuchert   60 

Strophomena    trentonensis    Win- 
chell  and    Schuchert 60 

Strophomena  trilobata  Owen....       64 
Strophomena  winchelli  Hall  and 

Clarke   60 

Structure-contour    map,    explana- 
tion of    107-108 

Structure    of    Dixon    quadrangle 

109-111 

origin  of    110-111 

pre-St.  Peter  Ill 

Subulites    regularis    Ulrich    and 

Scofield   60 

T 
Tealls   Corners,   preglacial  valley 

southeast  of   99 

Temperance     Hill     School,     sand 

dunes  near    79, 102 

Terraces   16 

Tertiary  peneplanation  90-93 

Thaleops  ovatus  Conrad 60 

Till,   age  of 70-73 

definition  of   27 

Topographic   map,   interpretation 

of    19-20 

Topography     13-18 

Transportation   18 

Trochonema  oeachi  Whitfield....       60 
Trochonema  umoilicatum  Hall..  60,  64 

U 
Upland  plain 13-14 


V 

PAGE 

Valleys    14-16 

"box"  valleys   15,  50 

limestone  valleys    14 

sandstone  valleys   15 

sandstone  with  overlying  lime- 
stone            15 

till  valleys    14 

Valley  slopes,  formation  of  asym- 
metrical     102-104 

Valley  train,  Early  Wisconsin...  76 
gravel  pit  in  Late  Wisconsin.  .  77 
Late  Wisconsin    77-78 

Vanuxemia  wortheni  Ulrich 64 

Vegetation    13 

W 

Water  analyses   116, 119 

Water    resources     of    the     quad- 
rangle     112-119 

ground    113-119 

surface    112-113 

Water  wells    114-119 

artesian    117-119 

in  limestone   115-116 

in  St.  Peter  sandstone 116-117 

shallow,   in   till 114-115 

Weathering,    definition    of 22 

Wells  in  quadrangle,   deep 70 

West    Dixon,    section    of    gravel 

pit  in    77 

Wisconsin    epoch    97-98 

Y 

Younger  Paleozoic  formations.  .  .65-66 

Z 

Zygospira,  nicoletti  Winchell  and 

Schuchert    60 

Zygospira  recurvirostris  Hall. ...       60 


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